fix(yamlfmt): Migrate to `doublestar` path discovery.

See also: gitlab-com/gl-infra/common-ci-tasks-images!454

Issue: gitlab-com/gl-infra/common-template-copier#6

yamlfmt.yml

@@ -13,14 +13,22 @@ yamlfmt:
   script:
     # yamlfmt will fail if this file doesn't exist.
     - touch .yamlfmtignore
+    - |
+      declare -a PATTERNS=('*.yaml' '*.yml')
+      if [[ -e .yamlfmtextra ]]; then
+        IFS=' '
+        while read -r pattern; do
+          PATTERNS+=("${pattern}")
+        done <<<$(grep -E -v '^\s*(#|$)' .yamlfmtextra)
+      fi
     - |
       # Dump yamlfmt config
       echo "# /etc/yamlfmt.yaml"
       cat /etc/yamlfmt.yaml
-    - yamlfmt -conf /etc/yamlfmt.yaml .
+    - yamlfmt -conf /etc/yamlfmt.yaml "${PATTERNS[@]}"
     - git diff | tee yamlfmt.patch
     - |
-      if [ -s yamlfmt.patch ]; then
+      if [[ -s yamlfmt.patch ]]; then
         red="$(printf "\e[31;1m")"
         reset="$(printf "\e[0m")"
         echo "${red}Some YAML files are not formatted correctly. Run the following command in the repository root to fix:${reset}"