roachtest: decommission/mixed-versions failed

[cockroach-teamcity]

roachtest.decommission/mixed-versions failed with artifacts on master @ 684e753c15f3fc58df79b6ea70e7b6715eae4835:

The test failed on branch=master, cloud=gce:
test artifacts and logs in: /home/agent/work/.go/src/github.com/cockroachdb/cockroach/artifacts/decommission/mixed-versions/run_1
	mixed_version_decommission.go:31,decommission.go:73,test_runner.go:777: prev version not set for version: 21.2
		(1) attached stack trace
		  -- stack trace:
		  | main.PredecessorVersion
		  | 	/home/agent/work/.go/src/github.com/cockroachdb/cockroach/pkg/cmd/roachtest/test_runner.go:1210
		  | main.runDecommissionMixedVersions
		  | 	/home/agent/work/.go/src/github.com/cockroachdb/cockroach/pkg/cmd/roachtest/mixed_version_decommission.go:29
		  | main.registerDecommission.func3
		  | 	/home/agent/work/.go/src/github.com/cockroachdb/cockroach/pkg/cmd/roachtest/decommission.go:73
		  | main.(*testRunner).runTest.func2
		  | 	/home/agent/work/.go/src/github.com/cockroachdb/cockroach/pkg/cmd/roachtest/test_runner.go:777
		  | runtime.goexit
		  | 	/usr/local/go/src/runtime/asm_amd64.s:1374
		Wraps: (2) prev version not set for version: 21.2
		Error types: (1) *withstack.withStack (2) *errutil.leafError

Reproduce

To reproduce, try:

# From https://go.crdb.dev/p/roachstress, perhaps edited lightly.
caffeinate ./roachstress.sh decommission/mixed-versions

Same failure on other branches

• roachtest: decommission/mixed-versions failed #58058 roachtest: decommission/mixed-versions failed [C-test-failure O-roachtest O-robot branch-release-20.2]

/cc @cockroachdb/kv

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