release-26.3: roachtest: follower-reads/mixed-version/survival=region/locality=global/reads=strong 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.follower-reads/mixed-version/survival=region/locality=global/reads=strong [failed](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Nightlies_Roachtests_RoachtestNightlyGcePrivateBazel/21467586?buildTab=log) with [artifacts](https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Nightlies_Roachtests_RoachtestNightlyGcePrivateBazel/21467586?buildTab=artifacts#/follower-reads/mixed-version/survival=region/locality=global/reads=strong) on release-26.3 @ [5d37df59f6d1be1e5832d53da78afecd7223b462](https://github.com/cockroachdb/cockroach/commits/5d37df59f6d1be1e5832d53da78afecd7223b462):

Failed with:

```
(follower_reads.go:360).runFollowerReadsTest: failed to get follower read counts: Get "https://10.91.96.253:26258/_status/vars": EOF
(mixedversion.go:926).Run: panic (stack trace above): t.Fatal() was called
test artifacts and logs in: /artifacts/follower-reads/mixed-version/survival=region/locality=global/reads=strong/run_1
```
Cluster Node to Ip Mapping:
| Node | Public IP | Private IP |
| --- | --- | --- |
| teamcity-21467586-1786857016-80-n6cpu4-geo-0001 | | 10.91.97.4 |
| teamcity-21467586-1786857016-80-n6cpu4-geo-0002 | | 10.91.96.48 |
| teamcity-21467586-1786857016-80-n6cpu4-geo-0003 | | 10.91.96.253 |
| teamcity-21467586-1786857016-80-n6cpu4-geo-0004 | | 10.91.128.113 |
| teamcity-21467586-1786857016-80-n6cpu4-geo-0005 | | 10.91.128.112 |
| teamcity-21467586-1786857016-80-n6cpu4-geo-0006 | | 10.91.48.63 |

Parameters:
- arch=amd64
- cloud=gce
- coverageBuild=false
- cpu=4
- diskCount=0
- encrypted=false
- fs=ext4
- localSSD=true
- mvtDeploymentMode=system-only
- mvtVersions=v26.2.0 → v26.3.1-dev-5d37df59f6d1be1e5832d53da78afecd7223b462 (release-26.3)
- 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-21467586/follower-reads-mixed-version-survival-region-locality-global-re/1786876308381/1786877207136)

See: [Datadog Logs](https://us5.datadoghq.com/logs?query=service%3Aroachtest+%40cluster%3Ateamcity-21467586-1786857016-80-n6cpu4-geo&from_ts=1786876308381&to_ts=1786877207136&live=false&storage=flex_tier)

/cc @cockroachlabs/kv-triage

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

Jira issue: CRDB-66730

Start with pkg/cmd/roachtest/follower_reads.go at line 360 and the mixed-version failure path reported at mixedversion.go:926. Review the linked test artifacts, logs, Grafana data, and Datadog logs to determine why the status-vars request returns EOF. Done means identifying and correcting the failure cause so the follower-reads mixed-version test passes without the reported panic.

Written by the indexing model from the issue text.