Corrected get_by_label to use only labels in the ontology #1807

Job	Run time
EMMO documentation (test using ontodoc)	3m 9s
pytest (3.7)	3m 16s
pytest (3.8)	4m 14s
pytest (3.9)	3m 29s
pytest (3.10)	3m 21s
pytest (3.11)	3m 42s
External / Run `pre-commit`	1m 32s
External / Build distribution package	34s
External / Build Documentation	1m 20s
External / Run `pylint` & `safety`	1m 50s
	26m 27s

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