chore(linux): Prevent building on s390x

This reverts commit 07ae306f which
got merged in PR #6500 after a discussion on the Debian mailing list.

However, Keyman currently doesn't work on s390x architecture because
we don't support big-endian (#5111). This shows in test failures during
package build (cf https://buildd.debian.org/status/fetch.php?pkg=keyman&arch=s390x&ver=16.0.138-4&stamp=1676139609&raw=0).