Bump third_party/imgui/repo from 2860d7b to 39585aa

Bumps [third_party/imgui/repo](https://github.com/ocornut/imgui) from `2860d7b` to `39585aa`.
- [Release notes](https://github.com/ocornut/imgui/releases)
- [Commits](ocornut/imgui@2860d7b...39585aa)

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

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

third_party/imgui/repo

@@ -0,0 +1 @@
+39585aa90d43c26a12a0d754d16b407f0c1ca62d