[dev.boringcrypto] misc/boring: skip long tests during build.release

[dev.boringcrypto] misc/boring: skip long tests during build.release

In CL 397477 I merged long tests into the built-in cmd/release flow.
Skip them during the boringcrypto release for now; we've never run them
before.

For #51797.

Change-Id: I8d5caa945a2558cd3a311a90be5bfb62ae7b0ace
Reviewed-on: https://go-review.googlesource.com/c/go/+/401338
Run-TryBot: Heschi Kreinick <heschi@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>