tidy-up: mostly whitespace nits

- delete completed TODO from `./CMakeLists.txt`.
- convert a C++ comment to C89 in `./CMake/CurlTests.c`.
- delete duplicate EOLs from EOF.
- add missing EOL at EOF.
- delete whitespace at EOL (except from expected test results).
- convert tabs to spaces.
- convert CRLF EOLs to LF in GHA yaml.
- text casing fixes in `./CMakeLists.txt`.
- fix a codespell typo in `packages/OS400/initscript.sh`.

Closes #11772

packages/OS400/initscript.sh

@@ -266,7 +266,7 @@ versioned_copy()
 #       The `sed' statement works as follows:
 #       - Join \nl-separated lines.
 #       - Retain only lines that begins with "identifier =".
-#       - Replace @...@ sustitutions by shell variable references.
+#       - Replace @...@ substitutions by shell variable references.
 #       - Turn these lines into shell variable assignments.
 
 get_make_vars()