Rename "Non-significant" to "Not for changelog".

The previous name was not universally liked, because technically a PR
might be very much significant, we just don't want to mention it in the
changelog.

.github/PULL_REQUEST_TEMPLATE.md

@@ -9,7 +9,7 @@ Changelog category (leave one):
 - Build/Testing/Packaging Improvement
 - Documentation (changelog entry is not required)
 - Other
-- Non-significant (changelog entry is not required)
+- Not for changelog (changelog entry is not required)
 
 
 Changelog entry (a user-readable short description of the changes that goes to CHANGELOG.md):

utils/make_changelog.py

@@ -284,7 +284,7 @@ def parse_one_pull_request(item):
     cat = re.sub(r'^[-*\s]*', '', cat)
 
     # Filter out the PR categories that are not for changelog.
-    if re.match(r'(?i)doc|((non|in|not|un)[-\s]*significant)', cat):
+    if re.match(r'(?i)doc|((non|in|not|un)[-\s]*significant)|(not[ ]*for[ ]*changelog)', cat):
         return False
 
     short_descr = ''

utils/simple-backport/format-changelog.py

@@ -57,7 +57,7 @@ def parse_one_pull_request(item):
         category = "NO CL CATEGORY"
 
     # Filter out the PR categories that are not for changelog.
-    if re.match(r'(?i)doc|((non|in|not|un)[-\s]*significant)', category):
+    if re.match(r'(?i)doc|((non|in|not|un)[-\s]*significant)|(not[ ]*for[ ]*changelog)', category):
         return False
 
     if not entry: