Improve GitHub Actions hazelcast membership check (#1530)

We restrict actions' execution to members of the `hazelcast`
organisation using `hazelcast/hazelcast-tpm/membership`, passing in the
user derviced from `github.event.pull_request.head.repo.owner.login`.

This is the owner of the repository, _not_ the user itself.

In the case of a non-fork PR - i.e. one in the `hazelcast` original repo
- the `owner` will be `hazelcast` (which _isn't_ a GitHub user, and
_isn't_ a member of the `hazelcast` organisation) and will fail.

This nuance prevented
hazelcast/hazelcast-python-client#720 from being
merged.

Instead we should query `github.actor` as [already used in the C++
client](https://github.com/hazelcast/hazelcast-cpp-client/blame/b63e40748aa8e06f790510d86e1eae87cc36925a/.github/workflows/build-pr.yml#L50).

Author: JackPGreen

.github/workflows/coverage_runner.yml

@@ -25,7 +25,7 @@ jobs:
         uses: hazelcast/hazelcast-tpm/membership@main
         with:
           organization-name: 'hazelcast'
-          member-name: ${{ github.event.pull_request.head.repo.owner.login }}
+          member-name: ${{ github.actor }}
           token: ${{ secrets.PAT }}
 
   run-tests: