[4.6.x] ci: use medium resource for validation

[mergify]

This is an automatic copy of pull request #13942 done by Mergify.

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Description

Validation of backend is taking more and more time in CI.
Currently on master branch, the average time is around 6min

Increasing resource from small to medium, increase he cost by 2, but divide the time by 3.

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Cherry-pick of 63dd7f8 has failed:

On branch mergify/bp/4.6.x/pr-13942
Your branch is up to date with 'origin/4.6.x'.

You are currently cherry-picking commit 63dd7f8432.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .circleci/ci/src/jobs/backend/job-validate.ts

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .circleci/ci/src/pipelines/tests/resources/bridge-compatibility-tests/bridge-compatibility-tests.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-4-1-x.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-custom-branch-backend-distribution-only.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-custom-branch-backend-gateway-only.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-custom-branch-backend-integration-tests-only.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-custom-branch-backend-only.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-custom-branch-backend-plugin-only.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-custom-branch-backend-rest-api-only.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-custom-branch.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-master.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-mergify.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-run-e2e.yml

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

[mergify]

Cherry-pick of 63dd7f8 has failed:

On branch mergify/bp/4.6.x/pr-13942
Your branch is up to date with 'origin/4.6.x'.

You are currently cherry-picking commit 63dd7f8432.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
	modified:   .circleci/ci/src/jobs/backend/job-validate.ts

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   .circleci/ci/src/pipelines/tests/resources/bridge-compatibility-tests/bridge-compatibility-tests.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-4-1-x.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-custom-branch-backend-distribution-only.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-custom-branch-backend-gateway-only.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-custom-branch-backend-integration-tests-only.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-custom-branch-backend-only.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-custom-branch-backend-plugin-only.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-custom-branch-backend-rest-api-only.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-custom-branch.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-master.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-mergify.yml
	both modified:   .circleci/ci/src/pipelines/tests/resources/pull-requests/pull-requests-run-e2e.yml

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally