69 grade me fix unit tests

[matthewhilton]

Fixes a number of unit test issues in newer versions of Moodle & Phpunit

• URL change from grade -> grader
• Removal of dbunit, replaced with equivalent functions
• Deprecation of assertRegexp, replaced with assertMatchesRegularExpression

Test output now:

vendor/bin/phpunit --testsuite=block_grade_me_testsuite --stop-on-failure
Moodle 4.1.2+ (Build: 20230318), cc547154ea691cf64d15743fc6f931906d4f5a5c
Php: 8.0.24, mysqli: 8.0.31, OS: Linux 5.19.0-35-generic x86_64
PHPUnit 9.5.27 by Sebastian Bergmann and contributors.

.........S........                                                18 / 18 (100%)

Time: 00:50.524, Memory: 95.00 MB

OK, but incomplete, skipped, or risky tests!
Tests: 18, Assertions: 46, Skipped: 1.

Closes #69