test: move BaseDetectorTest from Microsoft.ComponentDetection.Detectors.Tests to Microsoft.ComponentDetection.TestsUtilities

[JamieMagee]

BaseDetectorTest is the replacement for DetectorTestUtility. DetectorTestUtility was in the TestsUtilities namespace, however BaseDetectorTest was placed in the Detectors.Tests namespace. This change fixes that.

[github-actions]

👋 Hi! It looks like you modified some files in the Detectors folder.
You may need to bump the detector versions if any of the following scenarios apply:

• The detector detects more or fewer components than before
• The detector generates different parent/child graph relationships than before
• The detector generates different devDependencies values than before

If none of the above scenarios apply, feel free to ignore this comment 🙂