pkg/upgrade/upgrademanager/upgrademanager_test: TestConcurrentMigrationAttempts failed

pkg/upgrade/upgrademanager/upgrademanager_test.TestConcurrentMigrationAttempts [failed](https://mesolite.cluster.engflow.com/invocations/default/f9a3dfd5-dd60-4b61-be61-a4b40381ee6e?testReportRun=1&testReportShard=1&testReportAttempt=1#targets-Ly9wa2cvdXBncmFkZS91cGdyYWRlbWFuYWdlcjp1cGdyYWRlbWFuYWdlcl90ZXN0) on master @ [56d1013793884afefb9e4a9242e51425b695557f](https://github.com/cockroachdb/cockroach/commits/56d1013793884afefb9e4a9242e51425b695557f):

```
=== RUN TestConcurrentMigrationAttempts
test_log_scope.go:172: test logs captured to: outputs.zip/logTestConcurrentMigrationAttempts943816741
test_log_scope.go:82: use -show-logs to present logs inline
test_server_shim.go:95: cluster virtualization disabled due to issue: #107395 (expected label: C-bug)
```

Parameters:
- attempt=1
- race=true
- run=1
- shard=1
Help

See also: [How To Investigate a Go Test Failure \(internal\)](https://cockroachlabs.atlassian.net/l/c/HgfXfJgM)

/cc @cockroachlabs/release-eng @cockroachlabs/release-eng

[Improve this report!](https://github.com/cockroachdb/cockroach/tree/master/pkg/cmd/bazci/githubpost/issues)

Jira issue: CRDB-67658

Start with pkg/upgrade/upgrademanager/upgrademanager_test and TestConcurrentMigrationAttempts, reproducing the failure with race=true. Inspect the captured test logs from outputs.zip and the linked test report; done means the concurrent migration test passes reliably under the reported parameters.

Written by the indexing model from the issue text.