fix: regex should not be required

.github/workflows/reusable-clean-containers.yml

@@ -1,24 +1,25 @@
 name: Reusable container image cleanup
 on:
   workflow_call:
-      inputs:
-        package-name:
-          type: string
-          required: true
-          description: |
-           name of package/container to remove
-           starts with repository name e.g. base-images/centos
-        ignored-regex:
-          type: string
-          required: true
-          description: |
-            regex which is applied against image tags to ignore/keep those versions
-        number-kept:
-          type: number
-          required: true
-          default: 3
-          description: |
-            number of untagged versions to keep in package history
+    inputs:
+      package-name:
+        type: string
+        required: true
+        description: |
+          name of package/container to remove
+          starts with repository name e.g. base-images/centos
+      ignored-regex:
+        type: string
+        required: false
+        default: "^$"
+        description: |
+          optional regex which is applied against image name. The default matches nothing, so no versions are ignored
+      number-kept:
+        type: number
+        required: true
+        default: 3
+        description: |
+          number of untagged versions to keep in package history
 jobs:
   clean:
     runs-on: ubuntu-latest
@@ -29,8 +30,8 @@ jobs:
           exit 1
       - uses: actions/delete-package-versions@e5bc658cc4c965c472efe991f8beea3981499c55 #v5.0.0
         with:
-        # Can be a single package version id, or a comma separated list of package version ids.
-        # Defaults to an empty string.
+          # Can be a single package version id, or a comma separated list of package version ids.
+          # Defaults to an empty string.
           ignore-versions: ${{ inputs.ignored-regex }}
           # Owner of the package.
           # Defaults to the owner of the repo executing the workflow.