roachtest: ssh_problem failed

roachtest.ssh_problem [failed](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Nightlies_RoachtestNightlyGceBazel/21127061?buildTab=log) with [artifacts](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Nightlies_RoachtestNightlyGceBazel/21127061?buildTab=artifacts#/backup/2TB/n10cpu4) on release-25.2.14-rc @ [41623f2c082b258db3f86bf01f6371ce96245f97](https://github.com/cockroachdb/cockroach/commits/41623f2c082b258db3f86bf01f6371ce96245f97):

```
test backup/2TB/n10cpu4 failed: (test_runner.go:840).func4: cluster.PutE: put "/go/src/github.com/cockroachdb/cockroach/bin/cockroach.linux-arm64" failed: error persisted after 2 attempts: TRANSIENT_ERROR(ssh_problem): ~ scp -r -C -o StrictHostKeyChecking=no -o ConnectTimeout=10 -i /home/roach/.ssh/id_rsa /go/src/github.com/cockroachdb/cockroach/bin/cockroach.linux-arm64 ubuntu@136.119.145.10:./cockroach
Warning: Permanently added '136.119.145.10' (ECDSA) to the list of known hosts.
client_loop: send disconnect: Broken pipe
lost connection: exit status 1 [owner=test-eng]
```

Parameters:
- arch=arm64
- cloud=gce
- coverageBuild=false
- cpu=4
- diskCount=0
- encrypted=false
- fs=ext4
- localSSD=false
- runtimeAssertionsBuild=false
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-21127061/backup-2tb-n10cpu4/-62135596800000/-62135596680000)

Same failure on other branches

- #162299 roachtest: ssh_problem failed [O-roachtest O-robot T-testeng X-infra-flake branch-release-24.3.26-rc]
- #161667 roachtest: ssh_problem failed [O-roachtest O-robot T-testeng X-infra-flake branch-release-25.3.8-rc]
- #161664 roachtest: ssh_problem failed [O-roachtest O-robot T-testeng X-infra-flake branch-release-25.2.12-rc]
- #161602 roachtest: ssh_problem failed [O-roachtest O-robot T-testeng X-infra-flake branch-release-25.4.4-rc]
- #161498 roachtest: ssh_problem failed [O-roachtest O-robot T-testeng X-infra-flake branch-release-26.1.0-rc]
- #160756 roachtest: ssh_problem failed [O-roachtest O-robot T-testeng X-infra-flake branch-release-25.3.7-rc]
- #160426 roachtest: ssh_problem failed [O-roachtest O-robot T-testeng X-infra-flake branch-release-25.4.3-rc]
- #160363 roachtest: ssh_problem failed [O-roachtest O-robot T-testeng X-infra-flake branch-release-25.2.11-rc]
- #160157 roachtest: ssh_problem failed [O-roachtest O-robot T-testeng X-infra-flake branch-release-24.3.25-rc]
- #159400 roachtest: ssh_problem failed [O-roachtest O-robot T-testeng X-infra-flake branch-release-26.1]

/cc @cockroachdb/test-eng

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

Jira issue: CRDB-60520

Start with pkg/cmd/roachtest/README.md and the failure at test_runner.go:840, then inspect how the backup/2TB/n10cpu4 test uses cluster.PutE and reports ssh_problem. Review the linked TeamCity artifacts and Grafana data to determine the cause of the broken scp connection; done means the recurring failure is understood and an appropriate fix or mitigation is identified.

Written by the indexing model from the issue text.