[horde] Tests fail to run with repo Horde/Mail

[Mike]

When I try and run tests for Horde/mail using phpunit, I get this:

vendor/bin/phpunit
PHPUnit 11.5.55 by Sebastian Bergmann and contributors.

Runtime:       PHP 8.5.5
Configuration: /var/www/mail/phpunit.xml.dist

........EEEEEEEEEEEEE...............EEE.ESE....................  63 /  
158 ( 39%)
.E.EFE.......SSSSSSSSSSF......EEE............EEE.....EEEEEEEEEE 126 /  
158 ( 79%)
EEEEEEEEEEEEEEEEEEEEEEEEEEEEES..                                158 /  
158 (100%)

Time: 00:00.078, Memory: 10.00 MB

There were 66 errors:

1) Horde\Mail\AddressTest::testPersonalEncoded with data set #0 ('Foo  
<foo at example.com>', 'Foo')
Error: Class "Horde\Mail\Rfc2047" not found

<snip a bunch more errors>

All these errors refer to that same class, and I can see the file DOES  
exist in src/

I tried a few changes in composer.json and/or phpunit.xml.dist, but  
couldn't get it to work.

I'm not sure why it isn't finding that file.

Something must be wrong with my setup.  My assumption is that  
composer.json and phpunit.xml.dist are correct in the repo.

Mike