Update CI to Go 1.25 and golangci-lint v7

Bump GitHub Actions workflow to use Go 1.25 (remove older 1.23/1.24 matrix entries) and update actions/setup-go to 1.25. Upgrade golangci-lint action from v6 to v7 and pin the linter version to v2.1.6 instead of using latest to ensure reproducible linting.

Author: youhide

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        go-version: ["1.23", "1.24"]
+        go-version: ["1.25"]
 
     steps:
       - uses: actions/checkout@v4
@@ -41,9 +41,9 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: "1.24"
+          go-version: "1.25"
 
       - name: golangci-lint
-        uses: golangci/golangci-lint-action@v6
+        uses: golangci/golangci-lint-action@v7
         with:
-          version: latest
+          version: v2.1.6