CI: bump golangci-lint-action to v8 for Go 1.26 support

The v6 action installs golangci-lint v1.64.8, which is built with Go
1.24 and refuses to load a go.mod targeting 1.26. v8 installs the v2
linter; drop --timeout since v2 removed the flag and the 1m default.

Author: luthermonson

.github/workflows/ci.yml

@@ -39,7 +39,6 @@ jobs:
           go-version: '1.26'
           cache: true
       - name: golangci-lint
-        uses: golangci/golangci-lint-action@v6
+        uses: golangci/golangci-lint-action@v8
         with:
           version: latest
-          args: --timeout=5m