GH Actions: change PHAR building to reusable workflow #1505

Job	Run time
Build Phar on PHP: 5.4 / Build Phar on PHP: 5.4	31s
Build Phar on PHP: 5.5 / Build Phar on PHP: 5.5	34s
Build Phar on PHP: 5.6 / Build Phar on PHP: 5.6	1m 35s
Build Phar on PHP: 7.0 / Build Phar on PHP: 7.0	35s
Build Phar on PHP: 7.1 / Build Phar on PHP: 7.1	29s
Build Phar on PHP: 7.2 / Build Phar on PHP: 7.2	33s
Build Phar on PHP: 7.3 / Build Phar on PHP: 7.3	1m 23s
Build Phar on PHP: 7.4 / Build Phar on PHP: 7.4	32s
Build Phar on PHP: 8.1 / Build Phar on PHP: 8.1	1m 28s
Build Phar on PHP: 8.3 / Build Phar on PHP: 8.3	30s
Build Phar on PHP: 8.2 / Build Phar on PHP: 8.2	32s
Build Phar on PHP: 8.4 / Build Phar on PHP: 8.4	31s
Build Phar on PHP: nightly / Build Phar on PHP: nightly	25s
	9m 38s

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