fix(ci): Use runner GH_PUBLIC_RO token for sccache

Prioritise GH_PUBLIC_RO environment variable (configured on runner) over
github-token input to ensure all contributors can download sccache from
GitHub releases without hitting rate limits.

.forgejo/actions/setup-rust/action.yml

@@ -91,16 +91,18 @@ runs:
     - name: Debug GitHub token availability
       shell: bash
       run: |
-        if [ -z "${{ inputs.github-token }}" ]; then
+        if [ -n "$GH_PUBLIC_RO" ]; then
+          echo "✅ Using GH_PUBLIC_RO environment variable for sccache"
+        elif [ -z "${{ inputs.github-token }}" ]; then
           echo "⚠️ No GitHub token provided - sccache will use fallback download method"
         else
-          echo "✅ GitHub token provided for sccache"
+          echo "✅ Using github-token input for sccache"
         fi
 
     - name: Setup sccache
       uses: https://github.com/mozilla-actions/sccache-action@v0.0.9
       with:
-        token: ${{ inputs.github-token }}
+        token: ${{ env.GH_PUBLIC_RO || inputs.github-token }}
 
     - name: Cache build artifacts
       id: build-cache