LibWeb+LibTextCodec: Fix a few WPT encoding test failures #30927

Job	Run time
Linux, x86_64, Release, GNU / CI	5m 15s
Linux, x86_64, Sanitizer, Clang / CI	21m 50s
Windows, x86_64, Sanitizer, ClangCL / CI	5m 8s
Linux, x86_64, Fuzzers, Clang / CI	2m 35s
macOS, arm64, Sanitizer, Clang / CI	41m 37s
Linux, x86_64, All_Debug, Clang / CI	12m 21s
Linux, arm64, Sanitizer, Clang / CI	50m 31s
	2h 19m 17s

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