MINOR: Various small cleanups in group-coordinator (#21450) #243

Job	Run time
build / Configure Workflow	2s
build / Compile and Check (Merge Ref)	14m 12s
build / Load Test Catalog	36s
build / JUnit tests Java ${{ matrix.java }}${{ (((matrix.run-flaky == true) && ' (flaky)') \|\| '') }}${{ (((matrix.run-new == true) && ' (new)') \|\| '') }}	0s
build / CI checks completed	2s
build / Collate Test Catalog	0s
build / Update Test Catalog	-1s
	14m 51s

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