Parallel subtests share *ipn.Notify pointers (e.g. runningNotify).
When multiple subtests reached the same phase concurrently, they
all wrote to the shared notify's InitialStatus field without
synchronization, triggering the race detector.
Fix by shallow-copying *ipn.Notify before setting InitialStatus,
so each test iteration works on its own copy.
Updates #19380
Change-Id: I9dd40037e02146166f006f4f7c1ddcc47adba191
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
782c73bf41