fix openmodelica setup in Github action (#118) #21

Job	Run time
regression-test (1.6, x64, ubuntu-latest, stable)	26m 11s
regression-test (1.6, x64, ubuntu-latest, nightly)	24m 2s
regression-test (1.6, x64, ubuntu-latest, 1.21)	19m 16s
regression-test (1.6, x64, windows-latest, stable)	33m 53s
regression-test (1.6, x64, windows-latest, nightly)	38m 3s
regression-test (1.6, x64, windows-latest, 1.21)	37m 50s
regression-test (1.9, x64, ubuntu-latest, stable)	23m 14s
regression-test (1.9, x64, ubuntu-latest, nightly)	22m 31s
regression-test (1.9, x64, ubuntu-latest, 1.21)	20m 29s
regression-test (1.9, x64, windows-latest, stable)	31m 54s
regression-test (1.9, x64, windows-latest, nightly)	35m 21s
regression-test (1.9, x64, windows-latest, 1.21)	32m 1s
	5h 44m 45s

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