Bump third_party/imgui/repo from 2ab3946 to 902b8cc (project-chip#40437)

Bumps [third_party/imgui/repo](https://github.com/ocornut/imgui) from `2ab3946` to `902b8cc`.
- [Release notes](https://github.com/ocornut/imgui/releases)
- [Commits](ocornut/imgui@2ab3946...902b8cc)

---
updated-dependencies:
- dependency-name: third_party/imgui/repo
  dependency-version: 902b8cc39a7f15fdacb85ac69346238d0a889ec6
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Andrei Litvin <[email protected]>

Author: dependabot[bot]