roachtest: make disk bandwidth test manual only

[aadityasondhi]

This test is a little too noisy until we make further improvements to the disk bandwidth limiter.

Fixes: #136064.

Release note: None

[cockroach-teamcity]

This change is 

[aadityasondhi]

Reason for RC backport is #136950

[itsbilal]

LGTM

[aadityasondhi]

TFTRs!

bors r+

[craig]

Build succeeded:

• linux_amd64_build
• windows_build
• local_roachtest
• linux_arm64_build
• examples_orms
• macos_amd64_build
• acceptance
• linux_amd64_fips_build
• local_roachtest_fips
• docker_image_amd64
• unit_tests
• check_generated_code
• macos_arm64_build
• lint

[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 #136064: branch-release-24.3.1-rc.

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[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.

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error creating merge commit from 9952005 to blathers/backport-release-24.3.1-rc-137288: 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 24.3.1-rc failed. See errors above.

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