internal/imports: skip TestModeGetmodeVendor
internal/imports: skip TestModeGetmodeVendor

Test is broken by recent cmd/go vendoring changes. Skipping the test
case while we figure out what to do.

Updates golang/go#34826

Change-Id: I31a6f18e40420970251e25836edcf32c56c10ef5
Reviewed-on: https://go-review.googlesource.com/c/tools/+/200299
Run-TryBot: Jay Conrod <f3fadaedc813344da5ec13b41e26596889cc5baa@google.com>
Reviewed-by: Bryan C. Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>

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