doc: remove fixed tests from `why-error.md` #5666

Job	Run time
Style/format (ubuntu-latest, feat_os_unix)	11s
Style/spelling (ubuntu-latest, feat_os_unix)	50s
Style/lint (ubuntu-latest, feat_os_unix)	1m 31s
Style/lint (macos-latest, feat_os_macos)	1m 20s
Style/toml	19s
Style/lint (windows-latest, feat_os_windows)	3m 2s
	7m 13s

Provide feedback