RFR: 8284507: GHA: Only check test results if testing was not skipped

[Christoph Langer]

In GitHub Actions the step "Check that all tests executed successfully" will be marked as failing when the "Run tests" step did not run but some earlier step already failed. This is irritating and it can be corrected by doing the test check only if testing was not skipped.

Here is a link to such a test run where the check failed although the issue was with the cygwin installation: https://github.com/GoeLin/jdk11u-dev/runs/5788778433?check_suite_focus=true

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Commit messages:
 - Do not check for successful test execution when testing was skipped

Changes: https://git.openjdk.java.net/jdk/pull/8139/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8139&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8284507
  Stats: 8 lines in 1 file changed: 4 ins; 0 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8139.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8139/head:pull/8139

PR: https://git.openjdk.java.net/jdk/pull/8139