.github: disable generation of schema

There seems to be some caching issue.

Change-Id: Iafaf3441fc448cfc732525bbff961e0f7f406e67
Reviewed-on: https://cue-review.googlesource.com/c/cue/+/6304
Reviewed-by: CUE cueckoo <cueckoo@gmail.com>
Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>

.github/workflows/gen.go

@@ -1,3 +1,4 @@
 package workflows
 
-//go:generate go run cuelang.org/go/cmd/cue cmd genworkflows cuelang.org/go/internal/ci
+// Disable generation of this script for now.
+// go:generate go run cuelang.org/go/cmd/cue cmd genworkflows cuelang.org/go/internal/ci