Fix comparison bug with 'rc' versions in packaging.version (#11841).

I added some tests in 2105ab8553b7 and found no bug, but it turns out
that the doctest is not actually run.  While converting the doctest to
unittest style, I stumbled upon this bug again and this time applied the
code patch provided by Filip Gruszczyński.
diff --git a/Misc/NEWS b/Misc/NEWS
index 5fdd7b2..07599ad 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -508,6 +508,9 @@
 Library
 -------
 
+- Issue #11841: Fix comparison bug with 'rc' versions in packaging.version.
+  Patch by Filip Gruszczyński.
+
 - Issue #13447: Add a test file to host regression tests for bugs in the
   scripts found in the Tools directory.