chore: update Go toolchain and Nix configuration

.github/workflows/lint.yaml

@@ -16,7 +16,7 @@ jobs:
       - uses: actions/checkout@v7
       - uses: actions/setup-go@v7
         with:
-          go-version: 1.26.5
+          go-version-file: go.mod
       - name: go fix
         run: |
           go fix ./...