Bump external/Catch2 from df04df9 to efb3968 (#190)

Bumps [external/Catch2](https://github.com/catchorg/Catch2) from `df04df9` to `efb3968`.
- [Release notes](https://github.com/catchorg/Catch2/releases)
- [Commits](catchorg/Catch2@df04df9...efb3968)

---
updated-dependencies:
- dependency-name: external/Catch2
  dependency-type: direct:production
...

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