GH-113661: unittest runner: Don't exit 5 if tests were skipped (#113856)

The intention of exiting 5 was to detect issues where the test suite
wasn't discovered at all. If we skipped tests, it was correctly
discovered.

Lib/unittest/main.py

@@ -269,7 +269,7 @@ class TestProgram(object):
             testRunner = self.testRunner
         self.result = testRunner.run(self.test)
         if self.exit:
-            if self.result.testsRun == 0:
+            if self.result.testsRun == 0 and len(self.result.skipped) == 0:
                 sys.exit(_NO_TESTS_EXITCODE)
             elif self.result.wasSuccessful():
                 sys.exit(0)