tests: Raise timeouts for bufferiszero and crypto-tlscredsx509

tests: Raise timeouts for bufferiszero and crypto-tlscredsx509

On our gcov CI job, the bufferiszero and crypto-tlscredsx509
tests time out occasionally, making the job flaky. Double the
timeout on these two tests.

Cc: qemu-stable@nongnu.org
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2221
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-id: 20240312110815.116992-1-peter.maydell@linaro.org
(cherry picked from commit 55f7c6a5f2bd82e1d2d0eac6eee0185ce0451815)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>