[llvm] [CI][NFC] Refactor compute_platform_title into generate_test_report_lib (PR #166604)

[Igor Wodiany via llvm-commits]

IgWod-IMG wrote:

One of the pre-merge jobs on my PR has unexpectedly failed (https://github.com/llvm/llvm-project/actions/runs/19142383289/job/54710765868?pr=166794) with:

```
2025-11-06T16:35:29.2658830Z + python C:/_work/llvm-project/llvm-project/.ci/generate_test_report_github.py 0 C:/_work/llvm-project/llvm-project/build/test-results.1em3gujk.xml C:/_work/llvm-project/llvm-project/ninja.log
2025-11-06T16:35:29.3379761Z Traceback (most recent call last):
2025-11-06T16:35:29.3380319Z   File "C:\_work\llvm-project\llvm-project\.ci\generate_test_report_github.py", line 8, in <module>
2025-11-06T16:35:29.3381529Z     import generate_test_report_lib
2025-11-06T16:35:29.3382093Z   File "C:\_work\llvm-project\llvm-project\.ci\generate_test_report_lib.py", line 14, in <module>
2025-11-06T16:35:29.3383102Z     class FailureExplanation(TypedDict):
2025-11-06T16:35:29.3383653Z   File "C:\_work\llvm-project\llvm-project\.ci\generate_test_report_lib.py", line 17, in FailureExplanation
2025-11-06T16:35:29.3384689Z     reason: str | None
2025-11-06T16:35:29.3385040Z TypeError: unsupported operand type(s) for |: 'type' and 'NoneType'
2025-11-06T16:35:29.3506607Z ##[error]Process completed with exit code 1.
```

It seems it may be related to this change --- unless I broke something, but I cannot see any other problems in the log.

https://github.com/llvm/llvm-project/pull/166604