dev: Output PHPUnit results with TestDox format

I removed the TestDox output when upgrading to PHPUnit 10 because the
behaviour changed: TestDox is output at the end, once all the tests have
run. I found this useless and so I removed this output.

However, I now realize that it can help to understand the order in which
the tests are run. It can help to debug strange behaviour.

Reference: 4dd097d

Makefile

@@ -126,6 +126,7 @@ icons: ## Build the icons asset
 test: ## Run the test suite
 	$(PHP) ./bin/phpunit \
 		-c .phpunit.xml.dist \
+		--testdox \
 		$(COVERAGE) \
 		$(PHPUNIT_FILTER) \
 		$(PHPUNIT_FILE)