fix: target Linux runners instead of macOS

Add platform label to run on Linux runners with Docker support.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.woodpecker/pr.yml

@@ -2,6 +2,9 @@
 when:
   - event: pull_request
 
+labels:
+  platform: linux/amd64
+
 clone:
   - name: clone
     image: woodpeckerci/plugin-git

.woodpecker/release.yml

@@ -3,6 +3,9 @@ when:
   - event: push
     branch: main
 
+labels:
+  platform: linux/amd64
+
 clone:
   - name: clone
     image: woodpeckerci/plugin-git