Go: Ignore Go workspace file go.work

With Go 1.18, support for Go workspaces will land.
Go workspaces are configured in `go.work`, which
contains paths to local development versions of
modules and therefore is not expected to be
commited.

See:
* https://github.com/golang/go/issues/45713

Go.gitignore

@@ -13,3 +13,6 @@
 
 # Dependency directories (remove the comment below to include it)
 # vendor/
+
+# Go workspace file
+go.work