Only setup PGO tests when --pgo is enabled. (GH-14927)

(cherry picked from commit f0807ab24cbd13163bff7e0de3a97fe83584b80d)

Co-authored-by: Gregory P. Smith <greg@krypto.org>
diff --git a/Lib/test/libregrtest/main.py b/Lib/test/libregrtest/main.py
index 78b6790..2b6607d 100644
--- a/Lib/test/libregrtest/main.py
+++ b/Lib/test/libregrtest/main.py
@@ -215,8 +215,9 @@
 
         removepy(self.tests)
 
-        # add default PGO tests if no tests are specified
-        setup_pgo_tests(self.ns)
+        if self.ns.pgo:
+            # add default PGO tests if no tests are specified
+            setup_pgo_tests(self.ns)
 
         stdtests = STDTESTS[:]
         nottests = NOTTESTS.copy()