regrtest: always show before/after of modified env (#1407)

Buildbots don't run tests with -vv and so only log "xxx was modified
by test_xxx" which is not enough to debug such random issue. In many
cases, I'm unable to reproduce the warning and so unable to fix it.

Always logging the value before and value after should help to debug
such warning on buildbots.
(cherry picked from commit ec4b172)

Lib/test/regrtest.py

@@ -1267,10 +1267,9 @@ def __exit__(self, exc_type, exc_val, exc_tb):
                     print("Warning -- {} was modified by {}".format(
                                                  name, self.testname),
                                                  file=sys.stderr)
-                    if self.verbose > 1 and not self.pgo:
-                        print("  Before: {}\n  After:  {} ".format(
-                                                  original, current),
-                                                  file=sys.stderr)
+                    print("  Before: {}\n  After:  {} ".format(
+                                              original, current),
+                                              file=sys.stderr)
         return False