I'm getting

galera.galera_defaults 'innodb'          [ skipped ]  Test requires Galera library version >= 26.4.6

despite having 26.4.6 installed. It turns out that check_galera_version.inc no longer works. It uses a bunch or regexes to extract components of the requested and actual galera versions. I've added a debug printout as

SELECT @GALERA_VERSION, @GALERA_MAJOR_VERSION, @GALERA_MINOR_VERSION, @GALERA_RELEASE_VERSION

UNION ALL

SELECT @ACTUAL_GALERA_VERSION, @ACTUAL_GALERA_MAJOR_VERSION, @ACTUAL_GALERA_MINOR_VERSION, @ACTUAL_GALERA_RELEASE_VERSION;

it already had debug selects, I suggest to replace them with mine as above, the result is easier to read
The output was

26.4.6          26      4       6

4.6(r323e509)    4      4       6

That is, wsrep_provider_version now has a different format and regexes fail to parse it into a comparable representation.

I have a system Gentoo sys-cluster/galera-26.4.6