ci: increase openai parallelism to 14 [backport 3.18] (#15184)

Backport b4ed7fc from #15180 to 3.18.

## Description

I am seeing this job time out a lot, it has 42 venvs to run, if we bump
the parallelism a bit it should help.

## Testing

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## Risks

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-->

## Additional Notes

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Signed-off-by: Yun Kim <yun.kim@datadoghq.com>
Co-authored-by: Brett Langdon <brett.langdon@datadoghq.com>

Author: dd-octo-sts[bot]

tests/llmobs/suitespec.yml

@@ -143,7 +143,7 @@ suites:
     runner: riot
     snapshot: true
   openai:
-    parallelism: 10
+    parallelism: 14
     paths:
       - '@bootstrap'
       - '@core'