internal/lsp/regtest: Skip failing/flaky TestRegenerateCgo
internal/lsp/regtest: Skip failing/flaky TestRegenerateCgo

Something is making this test deterministically fail in some
environments, such as @bcmills' desktop.

Skip it while I build go at tip and debug.

Updates golang/go#39135

Change-Id: I1bf8c55c5cfca471a904de85936f504313094807
Reviewed-on: https://go-review.googlesource.com/c/tools/+/234480
Run-TryBot: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>
Reviewed-by: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>

golang/tools,golang/tools,golang/tools,golang/tools,golang/tools