hook: Allow tag:/[tag]/{tag} prefixes in subject

This hook didn't detect cap'd subject when prefixed with
tag:/[tag]/{tag} eg.

tag(scope): Subject cap check failed
[tag] Subject cap check failed
{tag} Subject cap check failed

'@(+([[:alnum:]])?(\(+([[:alnum:]])\)):|\[+([[:alnum:][:punct:]])\]|\{+([[:alnum:][:punct:]])\}|squash\!)'
matches the prefixes and removes it from subject line before checking.

Author: ahmubashshir

hook.sh

@@ -212,8 +212,10 @@ validate_commit_message() {
   # reset warnings
   WARNINGS=()
 
-  # capture the subject, and remove the 'squash! ' prefix if present
-  COMMIT_SUBJECT=${COMMIT_MSG_LINES[0]/#squash! /}
+  # capture the subject, and remove the 'squash! ', 'tag: ', '[tag] ' or '{tag} ' prefix if present
+  shopt -s extglob
+  COMMIT_SUBJECT=${COMMIT_MSG_LINES[0]/#@(+([[:alnum:]])?(\(+([[:alnum:]])\)):|\[+([[:alnum:][:punct:]])\]|\{+([[:alnum:][:punct:]])\}|squash\!) /}
+  shopt -u extglob
 
   # if the commit is empty there's nothing to validate, we can return here
   COMMIT_MSG_STR="${COMMIT_MSG_LINES[*]}"