gitlab-ci: move shellcheck to own job fenced by changes:

hooks/pre-commit

@@ -36,7 +36,7 @@ else
             *.rb)
                 RB_FILES+=" $f"
                 ;;
-            *.yml|.*.yml|.yamllint)
+            *.yml|*.yaml|.yamllint)
                 YML_FILES+=" $f"
                 ;;
             *)
@@ -66,7 +66,7 @@ cmd_exists() {
 }
 
 find_command() {
-	for name in $@; do
+	for name in "$@"; do
 		for suff in "3" "-3" "-python3" ""; do
 			cmd=${name}${suff}
 			if cmd_exists $cmd; then