.github/workflows: don't run latest deps against a locked Go version

They might require a newer Go version, but setup-go doesn't run again
after updating the go.mod file.

Author: FiloSottile

.github/workflows/test.yml

@@ -19,6 +19,9 @@ jobs:
         deps:
           - locked
           - latest
+        exclude:
+          - go: { go-version-file: go.mod }
+            deps: latest
     steps:
       - uses: actions/checkout@v5
         with: