gopls/internal/regtest/misc: temporarily skip TestGenerateProgress

For golang/go#49901

Change-Id: Id41c6437fadf1c539488662fc0ca5bc746b8a498
Reviewed-on: https://go-review.googlesource.com/c/tools/+/368216
Trust: Bryan C. Mills <bcmills@google.com>
Run-TryBot: Bryan C. Mills <bcmills@google.com>
Reviewed-by: Robert Findley <rfindley@google.com>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>

gopls/internal/regtest/misc/generate_test.go

@@ -16,6 +16,8 @@ import (
 )
 
 func TestGenerateProgress(t *testing.T) {
+	t.Skipf("skipping flaky test: https://golang.org/issue/49901")
+
 	const generatedWorkspace = `
 -- go.mod --
 module fake.test