net/http: skip TestClientTimeout_Headers_h{1,2} on windows/arm and windows/arm64

net/http: skip TestClientTimeout_Headers_h{1,2} on windows/arm and windows/arm64

This extends the skip added in CL 375635 to the "_Headers" variant of
the test, since we have observed similar failures in that variant on
the builders.

For #43120

Change-Id: Ib1c97fbb776b576271629272f3194da77913a941
Reviewed-on: https://go-review.googlesource.com/c/go/+/379156
Trust: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Damien Neil <dneil@google.com>