point setup-go cache at bskyweb/go.sum

The Go module lives in bskyweb/, not the repo root, so setup-go's
cache step couldn't find a dependencies file and skipped caching with
a warning. Point cache-dependency-path at bskyweb/go.sum.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.github/workflows/golang-test-lint.yml

@@ -20,6 +20,7 @@ jobs:
         uses: actions/setup-go@v6
         with:
           go-version-file: bskyweb/go.mod
+          cache-dependency-path: bskyweb/go.sum
       - name: Dummy Static Files
         run: touch bskyweb/static/js/blah.js && touch bskyweb/static/css/blah.txt && touch bskyweb/static/media/blah.txt
       - name: Check
@@ -37,6 +38,7 @@ jobs:
         uses: actions/setup-go@v6
         with:
           go-version-file: bskyweb/go.mod
+          cache-dependency-path: bskyweb/go.sum
       - name: Dummy Static Files
         run: touch bskyweb/static/js/blah.js && touch bskyweb/static/css/blah.txt && touch bskyweb/static/media/blah.txt
       - name: Lint