.gitlab: use less aggressive nproc on our aarch64/32 runners

.gitlab: use less aggressive nproc on our aarch64/32 runners

Running on all 80 cores of our aarch64 runner does occasionally
trigger a race condition which fails the build. However the CI system
is not the time and place to play with much heisenbugs so turn down
the nproc to "only" use 40 cores in the build.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220613171258.1905715-8-alex.bennee@linaro.org>