release-26.2: roachtest: backup-restore/mixed-version failed

**Note:** This build has runtime assertions enabled. If the same failure was hit in a run without assertions enabled, there should be a similar failure without this message. If there isn't one, then this failure is likely due to an assertion violation or (assertion) timeout.

roachtest.backup-restore/mixed-version [failed](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Nightlies_Roachtests_RoachtestNightlyGcePrivateBazel/21522022?buildTab=log) with [artifacts](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Nightlies_Roachtests_RoachtestNightlyGcePrivateBazel/21522022?buildTab=artifacts#/backup-restore/mixed-version) on release-26.2 @ [a06316c6e181a97cf6b3393b05b7b62daee04058](https://github.com/cockroachdb/cockroach/commits/a06316c6e181a97cf6b3393b05b7b62daee04058):

Failed with:

```
(mixedversion.go:926).Run: mixed-version test failure while running step 68 (run "plan and run backups"): retries exhausted waiting for job 1211283488344047618 to finish
test artifacts and logs in: /artifacts/backup-restore/mixed-version/run_1
```
Cluster Node to Ip Mapping:
| Node | Public IP | Private IP |
| --- | --- | --- |
| teamcity-21522022-1789710759-34-n5cpu4-0001 | | 10.91.96.86 |
| teamcity-21522022-1789710759-34-n5cpu4-0002 | | 10.91.96.133 |
| teamcity-21522022-1789710759-34-n5cpu4-0003 | | 10.91.100.210 |
| teamcity-21522022-1789710759-34-n5cpu4-0004 | | 10.91.100.209 |
| teamcity-21522022-1789710759-34-n5cpu4-0005 | | 10.91.97.135 |

Parameters:
- arch=amd64
- cloud=gce
- coverageBuild=false
- cpu=4
- diskCount=0
- encrypted=true
- fs=ext4
- localSSD=true
- mvtDeploymentMode=system-only
- mvtVersions=v25.2.23 → v25.3.7 → v25.4.16 → v26.1.8 → v26.2.7-dev-a06316c6e181a97cf6b3393b05b7b62daee04058 (release-26.2)
- runtimeAssertionsBuild=true
Help

See: [roachtest README](https://github.com/cockroachdb/cockroach/blob/master/pkg/cmd/roachtest/README.md)

See: [How To Investigate \(internal\)](https://cockroachlabs.atlassian.net/l/c/SSSBr8c7)

See: [Grafana](https://go.crdb.dev/roachtest-grafana/teamcity-21522022/backup-restore-mixed-version/1789713803065/1789730461969)

Same failure on other branches

- #175458 roachtest: backup-restore/mixed-version failed [A-disaster-recovery B-runtime-assertions-enabled C-test-failure O-roachtest O-robot P-2 T-disaster-recovery branch-master]
- #173774 release-26.3.1-rc: roachtest: backup-restore/mixed-version failed [A-disaster-recovery C-test-failure O-roachtest O-robot P-2 T-disaster-recovery branch-release-26.3.1-rc]
- #172161 roachtest: backup-restore/mixed-version failed [A-disaster-recovery B-runtime-assertions-enabled C-test-failure O-roachtest O-robot P-3 T-disaster-recovery branch-release-25.2]
- #170322 roachtest: backup-restore/mixed-version failed [A-disaster-recovery B-runtime-assertions-enabled C-test-failure O-roachtest O-robot P-2 T-disaster-recovery branch-release-26.1]

/cc @cockroachlabs/disaster-recovery

[This test on roachdash](https://roachdash.crdb.dev/?filter=status:open%20t:.*backup-restore/mixed-version.*&sort=title+created&display=lastcommented+project) | [Improve this report!](https://github.com/cockroachdb/cockroach/tree/master/pkg/cmd/bazci/githubpost/issues)

Jira issue: CRDB-68500

Start with the failure and logs under /artifacts/backup-restore/mixed-version/run_1, then read mixedversion.go around line 926 and the roachtest README. Investigate step 68, “plan and run backups,” including job 1211283488344047618; done means identifying the timeout cause and restoring a passing mixed-version backup-restore run.

Written by the indexing model from the issue text.