LibWeb+LibTextCodec: Fix a few WPT encoding test failures #30915

Job	Run time
Linux, x86_64, Release, GNU / CI	10m 4s
Linux, x86_64, All_Debug, Clang / CI	13m 32s
Linux, x86_64, Sanitizer, Clang / CI	22m 56s
Linux, arm64, Sanitizer, Clang / CI	47m 50s
macOS, arm64, Sanitizer, Clang / CI	33m 44s
Windows, x86_64, Sanitizer, ClangCL / CI	5m 21s
Linux, x86_64, Fuzzers, Clang / CI	11m 14s
	2h 24m 41s

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