backup: TestShowBackup failed

backup.TestShowBackup [failed](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Ci_TestsAwsLinuxArm64_UnitTests/21323489?buildTab=log) with [artifacts](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Ci_TestsAwsLinuxArm64_UnitTests/21323489?buildTab=artifacts#/) on master @ [9d7dcff5e0d36d1f0263fc0ef083185d5c6ca10b](https://github.com/cockroachdb/cockroach/commits/9d7dcff5e0d36d1f0263fc0ef083185d5c6ca10b):

```
=== RUN TestShowBackup
test_log_scope.go:172: test logs captured to: /artifacts/tmp/_tmp/6d8f0d953bcf81a6c6476724cd8eb3b1/logTestShowBackup1487715478
test_log_scope.go:82: use -show-logs to present logs inline
test_server_shim.go:168: automatically injected an external process virtual cluster under test; see comment at top of test_server_shim.go for details.
test_server_shim.go:637: DRPC is enabled (via testserver factory defaults)
test_server_shim.go:168: automatically injected a shared process virtual cluster under test; see comment at top of test_server_shim.go for details.
show_test.go:320: error executing query="BACKUP INTO LATEST IN $1;" args=["nodelocal://1/foo/full_cluster"]: pq: nodelocal://1/foo/full_cluster/incrementals/2026/04/22-212948.42/20260422/212949.83-20260422-212948.42 returned an unexpected error when checking for the existence of manifest: rpc error: code = Canceled desc = context canceled
testutils.go:368: no Invalid Descriptors
testutils.go:368: no Invalid Descriptors
panic.go:694: -- test log scope end --
test logs left over in: /artifacts/tmp/_tmp/6d8f0d953bcf81a6c6476724cd8eb3b1/logTestShowBackup1487715478
--- FAIL: TestShowBackup (16.29s)
```
Help

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

/cc @cockroachdb/disaster-recovery

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Jira issue: CRDB-63177