ci: use golangci-lint-action@v7 with v2.x linter

CI lint failed: action@v6 installed golangci-lint v1.64.8 (built with
go1.24), which can't parse the repo's version:"2" config and refuses to
run against the go 1.26.3 module directive. Bump to @v7 + pin v2.12.2
(the v2.x linter that passes locally). Tests were unaffected (all 3 OS
pass); this is a CI-tooling fix only.

Author: nixrajput

.github/workflows/ci.yml

@@ -36,6 +36,6 @@ jobs:
         with:
           go-version: stable
           cache: true
-      - uses: golangci/golangci-lint-action@v6
+      - uses: golangci/golangci-lint-action@v7
         with:
-          version: latest
+          version: v2.12.2