Prune idle sessions before starting new ones #646

Job	Run time
build (ubuntu-latest, Release)	4m 15s
build (ubuntu-latest, Debug)	3m 49s
build (windows-latest, Debug)	5m 45s
build (macos-latest, Debug)	3m 2s
build (macos-latest, Release)	2m 55s
build (windows-latest, Release)	4m 10s
publish-coverage	0s
build (windows-latest, Debug)	5m 45s
build (ubuntu-latest, Debug)	3m 57s
build (ubuntu-latest, Release)	3m 38s
build (macos-latest, Debug)	1m 39s
build (macos-latest, Release)	4m 5s
build (windows-latest, Release)	4m 10s
publish-coverage	0s
	47m 10s

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