Fix crash in PoolStateMachine+ConnectionGroup when closing connection while keepAlive is running #1099

Job	Run time
gh-codeql	3m 39s
gh-codeql	3m 39s
linux-integration-and-dependencies (postgres:16)	6m 10s
linux-integration-and-dependencies (postgres:16)	6m 10s
linux-unit (swift:5.7-jammy)	2m 14s
linux-unit (swift:5.7-jammy)	2m 14s
linux-integration-and-dependencies (postgres:14)	6m 9s
linux-integration-and-dependencies (postgres:14)	6m 9s
linux-unit (swift:5.8-jammy)	2m 10s
linux-unit (swift:5.8-jammy)	2m 10s
linux-integration-and-dependencies (postgres:12)	6m 11s
linux-integration-and-dependencies (postgres:12)	6m 11s
api-breakage	2m 58s
api-breakage	2m 58s
linux-unit (swift:5.9-jammy)	2m 28s
linux-unit (swift:5.9-jammy)	2m 28s
linux-unit (swiftlang/swift:nightly-5.10-jammy)	3m 0s
linux-unit (swiftlang/swift:nightly-5.10-jammy)	3m 0s
macos-all (postgresql@16, scram-sha-256, ~14.3)	2m 18s
macos-all (postgresql@16, scram-sha-256, ~14.3)	2m 18s
linux-unit (swiftlang/swift:nightly-main-jammy)	2m 54s
linux-unit (swiftlang/swift:nightly-main-jammy)	2m 54s
macos-all (postgresql@16, scram-sha-256, ~15.0)	3m 3s
macos-all (postgresql@16, scram-sha-256, ~15.0)	3m 3s
	1h 26m 28s

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