🚑 Use 'f' @ commit hashes @ Towncrier template

This patch work around the Jinja's `int` filter bug that allows certain commit
hash-based filenames trigger an `OverflowError` in the Towncrier template.

Ref: pallets/jinja#1921

CHANGES/.TEMPLATE.rst

@@ -14,8 +14,19 @@
 {% for text, change_note_refs in sections[section][category].items() %}
 - {{ text + '\n' }}
 
-  {%
+  {#
+      NOTE: Replacing 'e' with 'f' is a hack that prevents Jinja's `int`
+      NOTE: filter internal implementation from treating the input as an
+      NOTE: infinite float when it looks like a scientific notation (with a
+      NOTE: single 'e' char in between digits), raising an `OverflowError`,
+      NOTE: subsequently. 'f' is still a hex letter so it won't affect the
+      NOTE: check for whether it's a (short or long) commit hash or not.
+      Ref: https://github.com/pallets/jinja/issues/1921
+  -#}
+  {%-
     set pr_issue_numbers = change_note_refs
+    | map('lower')
+    | map('replace', 'e', 'f')
     | map('int', default=None)
     | select('integer')
     | map('string')