roachtest: deflake cdc/ledger

[andyyang890]

This patch deflakes cdc/ledger by increasing the target steady latency
from 1 minute to 3 minutes. It also eliminates a weird quirk where the
latency verifier expects the latency to be less than half of the target
latency before it'll be considered steady, which led to weird logs and
added unnecessary complexity.

Fixes #151381

Release note: None

[cockroach-teamcity]

This change is 

[andyyang890]

TC build showing 10 successful runs of cdc/ledger: https://teamcity.cockroachdb.com/buildConfiguration/Cockroach_Nightlies_RoachtestNightlyGceBazel/20702341?buildTab=tests

[log-head]

lgtm

[andyyang890]

TFTRs!

bors r=log-head,asg0451

[craig]

Build succeeded:

• linux_amd64_build
• unit_tests
• linux_amd64_fips_build
• check_generated_code
• local_roachtest
• local_roachtest_fips
• docker_image_amd64
• acceptance
• lint
• examples_orms

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

---

💡 Consider backporting to the fork repo instead of the main repo. See instructions for more details.

💡 Consider backporting to the fork repo instead of the main repo. See instructions for more details.

error creating merge commit from 08ce8f9 to blathers/backport-release-25.2-156985: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch release-25.2 failed. See errors above.

---

💡 Consider backporting to the fork repo instead of the main repo. See instructions for more details.

error creating merge commit from 08ce8f9 to blathers/backport-release-25.3-156985: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch release-25.3 failed. See errors above.

---

💡 Consider backporting to the fork repo instead of the main repo. See instructions for more details.

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}

[andyyang890]

Not seeing a merge conflict so I'll re-attempt with blathers

blathers backport 25.2 25.3

[blathers-crl]

Based on the specified backports for this PR, I applied new labels to the following linked issue(s). Please adjust the labels as needed to match the branches actually affected by the issue(s), including adding any known older branches.

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Issue #151381: branch-release-25.2, branch-release-25.3.

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_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}