support/testing: TestPerlDBDmysql: use ext2 instead of cpio

support/testing: TestPerlDBDmysql: use ext2 instead of cpio

The CPIO filesystem generated by TestPerlDBDmysql is too large, and
doesn't fit as an initramfs in the 256MB of RAM available in the
versatilepb machine. This causes a failure while running a basic
test "perl -MDBI -e '1'" since "/usr/lib/perl5", and many files
being missing from the root filesystem, ultimately causing the test
to fail.

Can't locate DBI.pm in @INC (you may need to install the DBI module)
(@INC entries checked: /usr/lib/perl5/site_perl/5.38.2/arm-linux
/usr/lib/perl5/site_perl/5.38.2 /usr/lib/perl5/5.38.2/arm-linux
/usr/lib/perl5/5.38.2).

It would make sense to switch all test cases to use ext2 + a
hard-drive, but for now, let's fix the few test cases that are causing
problems.

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/6735654506

Signed-off-by: Romain Naour <[email protected]>
Signed-off-by: Thomas Petazzoni <[email protected]>