Tests: Test-PSBuildPester

[HeyItsGilbert]

Add Pester 5 integration tests for Test-PSBuildPester.

Scenarios to cover:

• Invokes Pester against a fixture test file and returns a result object
• Correctly signals failure when tests fail (regression: Changes $configuration.Run.PassThru to $True #52)
• Code coverage output path and format are respected (regression: Addressing Issue #61 - update CodeCoverage Output File Format to fix error #62)
• Depends on shared fixture module (see Tests: Create shared fixture module #97

Parent issue: #17