Replace deprecated command with environment file

[jongwooo]

What this PR does / why we need it:

In workflow, set-output command is deprecated and will be disabled soon. For more information, see: https://github.blog/changelog/2022-10-11-github-actions-deprecating-save-state-and-set-output-commands/

litmus-helm/.github/workflows/main.yml

Lines 32 to 34 in 3f8e313

	run: |
	prsha=$(echo $response | jq '.[-1].sha' | tr -d '"')
	echo "::set-output name=sha::$prsha"

litmus-helm/.github/workflows/portal.yml

Lines 32 to 34 in 3f8e313

	run: |
	prsha=$(echo $response | jq '.[-1].sha' | tr -d '"')
	echo "::set-output name=sha::$prsha"

Which issue this PR fixes

(optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged)

• fixes Replace deprecated set-output command with environment file #392

Checklist

[Place an '[x]' (no spaces) in all applicable fields. Please remove unrelated fields.]

• DCO signed
• Chart Version bumped
• Variables are documented in the README.md