Improve the conversion of `Callable` to a string #318

Job	Run time
Code Coverage / Code Coverage	40s
Coding Standards / Coding Standards (8.0)	34s
Lint root / Lint yaml & Composer (8.0)	11s
Dependency analysis / Dependency Analysis (8.0)	21s
Unit test / Supported Versions Matrix	3s
Static analysis / Static Code Analysis (8.0)	37s
Unit test / Tests (8.0, locked)	33s
Unit test / Tests (7.4, locked)	52s
Unit test / Tests (7.4, lowest)	43s
Unit test / Tests (8.0, highest)	39s
Unit test / Tests (8.1, locked)	28s
Unit test / Tests (8.2, highest)	47s
Unit test / Tests (8.2, lowest)	42s
Unit test / Tests (8.2, locked)	43s
Unit test / Tests (7.4, highest)	45s
Unit test / Tests (8.0, lowest)	42s
Unit test / Tests (8.3, lowest)	42s
Unit test / Tests (8.1, highest)	39s
Unit test / Tests (8.4, locked)	44s
Unit test / Tests (8.1, lowest)	58s
Unit test / Tests (8.3, locked)	46s
Unit test / Tests (8.5, lowest)	42s
Unit test / Tests (8.5, highest)	37s
Unit test / Tests (8.4, lowest)	47s
Unit test / Tests (8.3, highest)	51s
Unit test / Tests (8.5, locked)	45s
Unit test / Tests (8.4, highest)	41s
	17m 32s

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