[CK] increase timeout limit for fmha_fwd tests to avoid CI
failure on gfx11 (#7471)
## Motivation
This should prevent fmha_fwd tests from timing out on one of the slower
gfx11 CI nodes and generating false CI failures.
## Technical Details
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## Test Plan
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## Test Result
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## Submission Checklist
- [ ] Look over the contributing guidelines at
https://github.com/ROCm/ROCm/blob/develop/CONTRIBUTING.md#pull-requests.
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