[CI] Add gfx950 FlyDSL Inductor test shard (#193473)

## Summary
- install the pinned FlyDSL 0.3.0 release wheel for the targeted CI job
- add a dedicated Inductor FlyDSL shard to the trunk gfx950 matrix
- fail early when the ROCm runtime or gfx950 device is unavailable instead of silently skipping GEMM coverage
- run the full FlyDSL template/GEMM test file; mock-only async compile tests remain covered by the existing default shards

## Test plan
- [x] `bash -n .ci/pytorch/common_utils.sh .ci/pytorch/test.sh`
- [x] `lintrunner --take SHELLCHECK .ci/pytorch/common_utils.sh .ci/pytorch/test.sh`
- [x] local gfx950 preflight with FlyDSL 0.3.0
- [x] `python test/run_test.py --include inductor/test_flydsl_template.py --verbose` (26 passed, 7 subtests passed)
- [ ] `ciflow/trunk`

Pull Request resolved: https://github.com/pytorch/pytorch/pull/193473
Approved by: https://github.com/jgong5, https://github.com/jansel
ghstack dependencies: #190903