CI: remove GHA cache from test job to fix buildx failure

The build job fails with "buildx failed with: </body></html>" because
both the test job and the reusable workflow write cache-to:type=gha,mode=max
for the same Docker context. This doubles cache pressure on GitHub's cache
API, which returns HTML error pages when hitting size/rate limits (known
issue docker/buildx#841). The reusable workflow already handles caching,
so the test job doesn't need its own cache directives.

https://claude.ai/code/session_01WY1ytdnf8Hrx3p7fnmZCUr

Author: claude

.github/workflows/docker.yml

@@ -10,7 +10,6 @@ on:
 
 permissions:
   contents: read
-  actions: write
 
 jobs:
   test:
@@ -31,8 +30,6 @@ jobs:
           push: false
           tags: dockette/coder:fx-test
           platforms: linux/amd64
-          cache-from: type=gha
-          cache-to: type=gha,mode=max
           load: true
 
       - name: Smoke test image