ci: bump go.yml to stable Go (go.mod requires 1.26.0; was pinned to 1.25.3)

Existing Tests workflow failed on the 1.26 toolchain requirement that
landed with the go.mod bump. Stable + check-latest matches what the
new ci-6arch.yml lane uses; the rest of the workflow (apt deps + SDL/
ebitengine builds + run_tests.sh) is unchanged.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: tannevaled

.github/workflows/go.yml

@@ -14,7 +14,8 @@ jobs:
     - name: Setup Go
       uses: actions/setup-go@v6
       with:
-        go-version: 1.25.3
+        go-version: stable
+        check-latest: true
     - name: Install dependencies
       run: |
         sudo apt-get update