internal/regtest/workspace: permanently skip TestDeleteModule_Interdependent

This test is flaky, likely due to some race in the
experimentalWorkspaceModule logic. Since we're about to delete support
for that experimental feature, simply skip the test to stop the flakes.

Leave the test as an artifact, as it will be deleted as part of the
clean up of experimentalWorkspaceModule. No need to delete it before
then.

Updates golang/go#55331
Fixes golang/go#55923

Change-Id: Ic17485e42e335459df462af00a2088812ecfb5f4
Reviewed-on: https://go-review.googlesource.com/c/tools/+/448116
Reviewed-by: Alan Donovan <adonovan@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
Run-TryBot: Robert Findley <rfindley@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Robert Findley <rfindley@google.com>

gopls/internal/regtest/workspace/workspace_test.go

@@ -335,7 +335,12 @@ func main() {
 
 // This change tests that the version of the module used changes after it has
 // been deleted from the workspace.
+//
+// TODO(golang/go#55331): delete this placeholder along with experimental
+// workspace module.
 func TestDeleteModule_Interdependent(t *testing.T) {
+	t.Skip("golang/go#55331: the experimental workspace module is scheduled for deletion")
+
 	const multiModule = `
 -- moda/a/go.mod --
 module a.com