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

tests/http/test_05_errors.py

@@ -108,4 +108,3 @@ class TestErrors:
         r.check_response(http_status=200, count=1)
         # check that we did a downgrade
         assert r.stats[0]['http_version'] == '1.1', r.dump_logs()
-