ci: build golangci-lint from source via goinstall

The action's prebuilt golangci-lint is compiled with an older Go and
refuses to analyze Go 1.26 code. install-mode: goinstall builds it with
the runner's toolchain instead.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Bharath-code

.github/workflows/ci.yml

@@ -53,3 +53,6 @@ jobs:
         uses: golangci/golangci-lint-action@v6
         with:
           version: latest
+          # Build golangci-lint with the repo's Go toolchain so it can analyze
+          # the targeted Go version (prebuilt binaries lag behind new releases).
+          install-mode: goinstall