[CI] Increase the MTEB_EMBED_TOL threshold to 5e-4.

[noooop]

Purpose

Increase the MTEB_EMBED_TOL threshold to 5e-4.

models/language/pooling_mteb_test/test_nemotron.py::test_embed_models_mteb[model_info0] in Language Models Test (MTEB) is a bit flaky lately.

https://buildkite.com/vllm/ci/builds/45475/steps/canvas?jid=019b8e61-5af4-47fe-b434-87827f0b7778
https://buildkite.com/vllm/ci/builds/45466/steps/canvas?jid=019b8d9c-2547-4e56-a104-6fa4e8077d85

There's a relatively high probability of encountering this.

Test Plan

models/language/pooling_mteb_test/

Test Result

pass

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Essential Elements of an Effective PR Description Checklist

• The purpose of the PR, such as "Fix some issue (link existing issues this PR will resolve)".
• The test plan, such as providing test command.
• The test results, such as pasting the results comparison before and after, or e2e results
• (Optional) The necessary documentation update, such as updating supported_models.md and examples for a new model.
• (Optional) Release notes update. If your change is user facing, please update the release notes draft in the Google Doc.

[gemini-code-assist]

Code Review

This pull request increases the tolerance for MTEB embedding tests from 1e-4 to 5e-4 to address test flakiness. Additionally, it removes explicit dtype="float32" configurations from several embedding model tests, allowing them to use the default auto dtype which typically resolves to a lower precision like float16. These changes are consistent, as using lower precision can lead to larger numerical differences, thus requiring a higher tolerance. The modifications seem reasonable for improving test stability and expanding test coverage to lower-precision data types. I have not found any issues with these changes.