fix: use portable grep -qw for word boundary in create-new-feature.sh

BSD grep (macOS) doesn't support \b as a word boundary. Replace with
grep -qw which is POSIX-portable.

Author: mnriem

extensions/git/scripts/bash/create-new-feature.sh

@@ -272,7 +272,7 @@ generate_branch_name() {
         if ! echo "$word" | grep -qiE "$stop_words"; then
             if [ ${#word} -ge 3 ]; then
                 meaningful_words+=("$word")
-            elif echo "$description" | grep -q "\b${word^^}\b"; then
+            elif echo "$description" | grep -qw -- "${word^^}"; then
                 meaningful_words+=("$word")
             fi
         fi