Fix JaCoCo coverage for multiple test tasks.

[singhmrinal02]

Addresses #18194.

What

I looked into this issue and found that the JaCoCo config was only
taking test.exec into account.

There are some other test tasks like needsRunnerTests and
validatesRunner which can also generate .exec files. Since those
files weren't being picked up, their coverage wasn't included in the
final report.

So I changed it to pick up all the .exec files from the build/jacoco
directory instead of only test.exec.

Testing

I ran:

• ./gradlew :buildSrc:compileGroovy — passed
• ./gradlew :runners:direct-java:needsRunnerTests — 997 tests completed,
  17 failed, 4 skipped

[singhmrinal02]

Hey! Just wanted to mention that this is actually my first ever open-source contribution. When I first opened the Beam project, I was honestly pretty overwhelmed and I’m still figuring things out.
If you get some time, I’d really appreciate some feedback on this PR — like what I did right, what I could have done better, or if I should have approached anything differently.
Also, any general tips on how I can become a better contributor and understand projects like this would be really helpful. I’m still pretty new to all of this and want to learn.
And if this isn’t something people usually ask in PRs, no worries . I just thought I’d ask since it’s my first contribution.

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