Bump tests/external/kissfft from `8f47a67` to `f5f2a3b` (#3341)

Bumps [tests/external/kissfft](https://github.com/mborgerding/kissfft) from `8f47a67` to `f5f2a3b`.
- [Release notes](https://github.com/mborgerding/kissfft/releases)
- [Commits](8f47a67f59...f5f2a3b2f2)

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

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tests/external/kissfft

@@ -1 +1 @@
-Subproject commit 8f47a67f595a6641c566087bf5277034be64f24d
+Subproject commit f5f2a3b2f2cd02bf80639adb12cbeed125bdf420