Update clang-format to include outcome

Author: Bill-hbrhbr

src/.clang-format

@@ -1,12 +1,12 @@
 BasedOnStyle: "InheritParentConfig"
 
 IncludeCategories:
-  # NOTE: A header is grouped by first matching regex library headers. Update when adding new 
+  # NOTE: A header is grouped by first matching regex library headers. Update when adding new
   # libraries.
   # NOTE: clang-format retains leading white-space on a line in violation of the YAML spec.
   - Regex: "<(ystdlib)"
     Priority: 3
-  - Regex: "<(catch2)"
+  - Regex: "<(catch2|outcome)"
     Priority: 4
   # C system headers
   - Regex: "^<.+\\.h>"