roachtest: use spot VM for all tests

[nameisbhaskar]

Currently, we are using spot VMs only to run benchmark tests. The reason for the low adoption of spot VM is because of the test failures due to VM preemption.
But, with the recent changes, we have better control on VM preemption changes where if there is a test failure due to preemption, the test is run on an on-demand VM the next time.
Also, the current failed tests that are run on spot VM is 148 out of 1093 = 13.5%. If I consider failure out of total tests run is 148 out of 2508 = 5.9%.

So, this PR removes the condition to use spot VMs only for benchmark tests and changes the probability to 75%.

Fixes: #127236
Epic: None

[cockroach-teamcity]

This change is 

[nameisbhaskar]

Ran 2 teamcity builds. The failure is ~13%
Test 1 - 28 tests out of 215 tests ran on spot VMs
Test 2 - 27 tests out of 208 tests ran on spot VMs

[shailendra-patel]

LGTM

[nameisbhaskar]

Thanks @shailendra-patel and @vidit-bhat for approving the change.

[nameisbhaskar]

bors r=@shailendra-patel,@vidit-bhat

[craig]

Build succeeded:

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

[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 #127236: branch-release-24.1, branch-release-24.2.

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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 69da7de to blathers/backport-release-24.1-127896: 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 24.1.x failed. See errors above.

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error creating merge commit from 69da7de to blathers/backport-release-24.2-127896: 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 24.2.x failed. See errors above.

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

[nameisbhaskar]

blathers backport 24.1 24.2

[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.

---

error creating merge commit from 69da7de to blathers/backport-release-24.1-127896: 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 24.1 failed. See errors above.

---

error creating merge commit from 69da7de to blathers/backport-release-24.2-127896: 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 24.2 failed. See errors above.

---

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