Fix PHPUnit GitHub actions (#388)

* Specify composer as the phpunit bootstrap

The PHPUnit action says the [default bootstrap is
vendor/autoload.php](https://github.com/marketplace/actions/phpunit-php-actions#inputs)
but it seems that the composer autoload was not called.

* Autoload CAS.php for tests

The CAS.php file defines a number of constants used by tests. Because
tests call directly into the underlying class and do not pass through
the CAS.php entrypoint, these constants are not defined in tests.

Author: francoisfreitag

.github/workflows/test.yml

@@ -35,6 +35,7 @@ jobs:
           php_version: "${{ matrix.php-version.php }}"
           php_extensions: xdebug
           args: --verbose --coverage-clover=coverage.xml
+          bootstrap: vendor/autoload.php
         env:
           XDEBUG_MODE: coverage
       - name: Report coverage

composer.json

@@ -36,6 +36,7 @@
 		]
 	},
 	"autoload-dev" : {
+		"files": ["source/CAS.php"],
 		"psr-4" : {
 			"PhpCas\\" : "test/CAS/"
 		}