feat(action): add workaround for private repos

This is a slow, but foolproof way to ensure a comparison report is
generated.

action.yml

@@ -46,6 +46,15 @@ inputs:
       The name of the job running this action. If not set, no comparisons can
       be made.
     default: ''
+  private-repo-workaround:
+    description: |
+      Forgejo doesn't support downloading artifacts through the API [see
+      codeberg.org/forgejo/forgejo#6315](https://codeberg.org/forgejo/forgejo/issues/6315).
+
+      As a workaround, checkout the base branch and regenerate the report.
+
+      This is very innefficient T-T and slow.
+    default: 'false'
 outputs:
 runs:
   using: 'composite'
@@ -65,6 +74,7 @@ runs:
         ARTIFACT_NAME: ${{ inputs.artifact-name }}
         HEAD_BRANCH: ${{ inputs.base-branch }}
         JOB_NAME: ${{ inputs.job-name }}
+        PRIVATE_REPO: ${{ inputs.private-repo-workaround }}
       run: |
         . "${GITHUB_ACTION_PATH}/utils.sh"
 
@@ -87,8 +97,17 @@ runs:
           test "$http_code" = '200'
         }
 
+        if [ "$PRIVATE_REPO" = 'true' ]; then 
+          log "In a private repo, switching to $HEAD_BRANCH to build the old report"
+          git switch "$HEAD_BRANCH"
+
+          "$GITHUB_ACTION_PATH/create-report.sh" > old-report.json
+
+          log "Reporting on sizes and comparing to sizes in $HEAD_BRANCH"
+          "$GITHUB_ACTION_PATH/comment_on_pr.sh" report.json old-report.json
+          exit 0
         # If we have a previous report compare against it
-        if [ "$JOB_NAME" ] && [ "$HEAD_BRANCH" ]; then
+        elif [ "$JOB_NAME" ] && [ "$HEAD_BRANCH" ]; then
           url=$(base_report_url)
           log "Found previous run at: $url"
           report_url="$url/artifacts/$ARTIFACT_NAME"