[`pyupgrade`] Prevent infinite loop with `I002` and `UP026` (#20634)
## Summary
Closes #20601
Do not treat imports as unused for the rule [unnecessary-builtin-import
(UP029)](https://docs.astral.sh/ruff/rules/unnecessary-builtin-import/)
if they are required by
`isort`([missing-required-import](https://docs.astral.sh/ruff/rules/missing-required-import/))
## Test Plan
- Added test case `i002_up029_conflict` to ensure there is no conflict
Co-authored-by: Igor Drokin <drokinii1017@gmail.com>