Add IGListTestCollectionViewLayout class to XCTest suite #126

Job	Run time
Verify Carthage build XCFramework	3m 6s
CocoaPods Lint	2m 54s
Build Examples and UI tests. (platform=iOS Simulator,name=iPhone 14 Pro,OS=16.4, platform=tvOS Si...	13m 3s
Verify Carthage build lipo binaries	3m 40s
Run Danger	0s
Unit Test iOS (platform=iOS Simulator,name=iPhone 14 Pro)	6m 4s
Unit Test macOS	2m 19s
Verify SPM build by invoking `xcodebuild` on Package.swift (IGListDiffKit)	39s
Verify generate_spm_sources_layout.sh is not broken	43s
Verify SPM build by invoking `xcodebuild` on Package.swift (IGListKit)	38s
Verify SPM build by invoking `xcodebuild` on Package.swift (IGListSwiftKit)	50s
	33m 56s

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