GH Action: Add steps to test against libxml >= 2.12 #2379

Job	Run time
Coverage: 8.4 (Linux)	4m 22s
Coverage: 8.4 (Win)	1m 29s
Coverage: 5.4 (Linux)	27m 31s
Coverage: 5.5 (Win)	3m 6s
Coverage: 7.2 with custom ini settings (Linux)	6m 13s
Build Phar on PHP: 8.0 / Build Phar on PHP: 8.0	20s
PHP: 5.4 (Linux)	1m 35s
PHP: 7.0 with custom ini settings (Linux)	1m 36s
PHP: 5.5 with custom ini settings (Linux)	7m 35s
PHP: 5.5 (Linux)	8m 54s
PHP: 5.6 (Linux)	7m 0s
PHP: 7.0 (Linux)	2m 12s
PHP: 7.1 (Linux)	1m 33s
PHP: 7.2 (Linux)	1m 25s
PHP: 7.3 (Linux)	53s
PHP: 7.4 (Linux)	1m 6s
PHP: 8.0 (Linux)	50s
PHP: 8.1 (Linux)	50s
PHP: 8.2 (Linux)	54s
PHP: 8.3 (Linux)	54s
PHP: 8.4 (Linux)	46s
PHP: 8.5 (Linux)	51s
PHP: 5.5 (Win)	1m 40s
PHP: 5.6 (Win)	6m 53s
PHP: 7.0 (Win)	1m 43s
PHP: 7.1 (Win)	1m 30s
PHP: 7.2 (Win)	1m 26s
PHP: 7.3 (Win)	53s
PHP: 7.4 (Win)	54s
PHP: 8.0 (Win)	52s
PHP: 8.1 (Win)	51s
PHP: 8.2 (Win)	51s
PHP: 8.3 (Win)	53s
PHP: 8.5 (Win)	52s
PHP: 8.4 (Win)	37s
coveralls-finish	2s
	1h 41m 52s

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