Document why files are excluded #2155

Job	Run time
Coding Guidelines	24s
Dependency Validation	10s
Type Checker	27s
Unit Tests (ubuntu-latest, 8.1)	10s
Unit Tests (ubuntu-latest, 8.2)	18s
Unit Tests (ubuntu-latest, 8.3)	13s
Unit Tests (ubuntu-latest, 8.4)	10s
Unit Tests (windows-latest, 8.1)	35s
Unit Tests (windows-latest, 8.2)	34s
Unit Tests (windows-latest, 8.3)	43s
Unit Tests (windows-latest, 8.4)	35s
End-to-End Tests (ubuntu-latest, 8.1)	33s
End-to-End Tests (ubuntu-latest, 8.2)	39s
End-to-End Tests (ubuntu-latest, 8.3)	34s
End-to-End Tests (ubuntu-latest, 8.4)	36s
End-to-End Tests (windows-latest, 8.1)	1m 34s
End-to-End Tests (windows-latest, 8.2)	1m 30s
End-to-End Tests (windows-latest, 8.3)	1m 27s
End-to-End Tests (windows-latest, 8.4)	1m 36s
Build PHAR	33s
Code Coverage	1m 57s
Test PHAR (8.1, pcov)	23s
Test PHAR (8.1, xdebug)	32s
Test PHAR (8.2, pcov)	24s
Test PHAR (8.2, xdebug)	29s
Test PHAR (8.3, pcov)	16s
Test PHAR (8.3, xdebug)	29s
Test PHAR (8.4, pcov)	24s
Test PHAR (8.4, xdebug)	31s
	18m 46s

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