Fix PHP 8.1 tests and confirm compatibility

[mrook]

We have a few tests failing on PHP 8.1, those need to be fixed (dependency on VersionControl_Git).

Also confirm 3.0 runs on 8.1 without issues.

• Update to newer VersionControl_Git
• Ignore PDepend tests on 8.1
• Select PHPUnit 9.5.10 as lowest to fix mocking issues in 8.1

[siad007]

Related to pear/VersionControl_Git#18

[mrook]

Update:

• VersionControl_Git was fixed
• PDepend doesn't support 8.1 yet (so we should probably ignore these tests on 8.1)
• The PHPUnit version we're selecting in lowest has mocking issues in 8.1