ci: bump build-and-test go-version 1.24->1.25 for setup-go@v6

setup-go@v6 defaults GOTOOLCHAIN=local, blocking the auto-upgrade from
the pinned 1.24 to go.mod's required 1.25.0. Bump the pin to match go.mod.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: claude

.github/workflows/ci.yml

@@ -73,7 +73,7 @@ jobs:
 
       - uses: actions/setup-go@v6
         with:
-          go-version: '1.24'
+          go-version: '1.25'
 
       - run: go build ./...
       - run: go vet ./...