ci: stop running the test matrix through castor

The PHP 8.2 and 8.3 jobs died before PHPUnit started:

    Castor requires PHP >= 8.4.0, but you are running PHP 8.2.31.

The matrix is the only place where the container image varies; every
other castor call runs on phpqa:8.4 and is fine. The job already installs
its own dependencies, so it now invokes the same PHPUnit binary castor
would have, without the wrapper that cannot run there.

Like the rest of this branch, the failure was invisible until now: the
test job is gated behind the analysis jobs and was skipped whenever one
of them failed.

Author: Spomky

.github/workflows/ci.yml

@@ -205,7 +205,11 @@ jobs:
           fi
 
       - name: Run PHPUnit
-        run: castor phpunit
+        run: |
+          composer exec -- phpunit-11 \
+            --coverage-xml .ci-tools/coverage \
+            --log-junit=.ci-tools/coverage/junit.xml \
+            --configuration .ci-tools/phpunit.xml.dist
 
   infection:
     name: "🧬 Mutation Testing"