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 ./...

.github/workflows/release.yaml

@@ -88,12 +88,12 @@ jobs:
         run: |
           echo "VERSION=$(git describe --tags --always)" >> $GITHUB_ENV
           echo "GIT_COMMIT=$(git rev-parse HEAD)" >> $GITHUB_ENV
-          echo "GO_VERSION=1.26.5" >> $GITHUB_ENV
+          echo "GO_VERSION=$(sed -n 's/^go //p' go.mod)" >> $GITHUB_ENV
 
       - name: Set up Go
         uses: actions/setup-go@v7
         with:
-          go-version: ${{ env.GO_VERSION }}
+          go-version-file: go.mod
           cache: true
 
       - name: Build binaries