Disable arch-specific autopkgtest if corresponding builds are disabled
Since 42e6a678, pipelines that set
SALSA_CI_DISABLE_BUILD_PACKAGE_I386: 1
cannot be created unless they
also explicitly set SALSA_CI_DISABLE_AUTOPKGTEST_I386: 1
. While it
might be possible to deal with this by changing all such packages,
that's a lot of churn, and it seems better to handle it automatically.