gh-actions: go version file

Author: ignoramous

.github/workflows/go.yml

@@ -36,10 +36,10 @@ jobs:
     - name: 🥏 Checkout code
       uses: actions/checkout@v6
 
-    - name: 🐼 Setup go1.26+
+    - name: 🐼 Setup Go
       uses: actions/setup-go@v6
       with:
-        go-version: '>=1.26'
+        go-version-file: 'go.mod'
         check-latest: true
 
     - name: 🏗️ Make
@@ -457,7 +457,7 @@ jobs:
       - name: 🐼 Set up Go
         uses: actions/setup-go@v6
         with:
-          go-version: '>=1.26'
+          go-version-file: 'go.mod'
           cache: false
       # github.com/tailscale/tailscale/blob/93324cc7b/.github/workflows/depaware.yml
       # consolidated in: github.com/tailscale/tailscale/commit/4022796484