Revert "Mark swift-protobuf-plugin-example as XFAIL until rdar://90955872 is fixed"

[abertelrud]

SwiftPM has now been fixed.

This reverts commit 0c90004.

[abertelrud]

@swift-ci please test

[abertelrud]

@swift-ci please test

[abertelrud]

Not quite sure why this is failing.

I see the swift-protobuf-plugin-example passing now (which is good, that's what this PR addresses):

PASS: swift-protobuf-plugin-example, 5.0, 85bec0, Swift Package

but then there is a UPASS which I'm fixing in a different PR:

========================================
UPasses:
  UPASS: https://bugs.swift.org/browse/SR-13190, SRP, 5.0, 8d2561, Swift Package
========================================
Action Summary:
     Passed: 333
     Failed: 0
    XFailed: 19
    UPassed: 1
      Total: 353
========================================
Repository Summary:
      Total: 113
========================================
Result: UPASS
========================================

and then a failure:

Traceback (most recent call last):
  File "./swift-source-compat-suite/run", line 325, in <module>
    sys.exit(main())
  File "./swift-source-compat-suite/run", line 52, in main
    execute_runner(workspace, args, additional_runner_args)
  File "./swift-source-compat-suite/run", line 217, in execute_runner
    common.check_execute(runner_command, timeout=9999999)
  File "/Users/ec2-user/jenkins/workspace/swift-PR-source-compat-suite-test-macOS/swift-source-compat-suite/common.py", line 407, in check_execute
    raise ExecuteCommandFailure(command, returncode)
common.ExecuteCommandFailure: ExecuteCommandFailure(command="./runner.py --swiftc /Users/ec2-user/jenkins/workspace-private/swift-PR-source-compat-suite-test-macOS/build/compat_macos/install/toolchain/usr/bin/swiftc --projects projects.json --include-actions 'action.startswith("Build")' --swift-branch main --sandbox-profile-xcodebuild ../../../workspace-private/swift-source-compat-suite-sandbox/sandbox_xcodebuild.sb --sandbox-profile-package ../../../workspace-private/swift-source-compat-suite-sandbox/sandbox_package.sb --build-config=release", returncode=1)

@shahmishal Is that failure because of the remaining UPASS? It's being fixed by #657, do I need to do a cross-branch test build to get that fix included here so there are no UPASSes in order for this to succeed?