Improve/fix GitHub Actions pipleline

[NamedPython]

Problems

• Compatibility problem at the java setup
• main.yml refers main branch, but default branch is master here.
• There're no checks at the PR

Solutions

• use setup-java@v4 and specify Java 8 and zulu distribution
• fix main reference to master
• split pipeline into gem-push and check. check will exec test at PullReq.

[chikamura]

You might need to set up JDK 8 and ruby 2.7.

https://github.com/trocco-io/embulk-input-jira/blob/7ebeebcdb00f4a783334bbbbd6d27b91ab764aa6/.github/workflows/gem-push.yml

      - name: Set up Ruby 2.7
        uses: ruby/setup-ruby@v1
        with:
          ruby-version: 2.7
      - name: Set up JDK 1.8
        uses: actions/setup-java@v4
        with:
          java-version: 8
          distribution: "zulu"

[chikamura]

If possible, it would be ideal to prevent gem push unless all tests have passed.

[chikamura]

LGTM

[IMO] The tests in check.yml and gem-push.yml are duplicated, so it may be better to merge them into a single file.

[NamedPython]

@chikamura I think that's better to know the lint / test failings before merge. Thanks for your review, gonna merge.