build: catch2 updated to 2.13.4

docs/CHANGELOG.md

@@ -20,6 +20,7 @@
   - (!) build: `BUILD_DOCS` CMake option renamed to `UNITS_BUILD_DOCS`
   - (!) build: `-g cmake_paths` has to be manually provided for `conan install` command (workaround for a Conan bug)
   - build: doxygen updated to 1.8.20
+  - build: catch2 updated to 2.13.4
   - build: Conan generator switched to `cmake_find_package_multi`
   - build: Conan CMakeToolchain support added
   - build: CMake scripts cleanup