backport: #20145: assertRaisesRegexp now raises a TypeError on bad regex.

Previously a non-string, non-regex second argument and no callable
argument could cause the test to appear to always pass.
diff --git a/Misc/NEWS b/Misc/NEWS
index 0f45555..711c70c 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -40,6 +40,9 @@
 Library
 -------
 
+- Issue #20145: `assertRaisesRegex` now raises a TypeError if the second
+  argument is not a string or compiled regex.
+
 - Issue #21058: Fix a leak of file descriptor in tempfile.NamedTemporaryFile(),
   close the file descriptor if os.fdopen() fails