Use --group filter for MW master phpunit run

The previous -c extensions/Bootstrap/ flag made PHPUnit load Bootstrap's
phpunit.xml.dist, which has no bootstrap directive, so MediaWiki was
never initialised and $GLOBALS['wgResourceModules'] was undefined when
BootstrapManagerTest read it.

Drop -c so MW's generated phpunit.xml (which wires up
tests/phpunit/bootstrap.php) is used, and filter to Bootstrap tests via
their @group annotation. Mirrors the Chameleon CI pattern.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: malberts

.github/workflows/ci.yml

@@ -97,4 +97,4 @@ jobs:
             wget -q -O phpunit.xml.template "https://raw.githubusercontent.com/wikimedia/mediawiki/${{ matrix.mw }}/phpunit.xml.template"
           fi
           composer phpunit:config
-          vendor/bin/phpunit -c extensions/Bootstrap/
+          vendor/bin/phpunit --group extension-bootstrap