chore(gha): fix macos action/setup-go@v4 cache miss.

Set the same Go version as specified in the `go.mod`
because of the issue below:
- actions/setup-go#424

Signed-off-by: Tiago Natel <t.nateldemoura@gmail.com>

go.mod

@@ -1,6 +1,6 @@
 module github.com/terramate-io/terramate
 
-go 1.18
+go 1.20
 
 require (
 	github.com/alecthomas/kong v0.7.1