The flag `Werror=unrecognised-warning-flags` does not turn unrecognised warnings on fatal errors

By running on GHC 9.2.3

ghc -Werror -Wunrecognised-warning-flags -Wfoo Main.hs

I got a compilation error as expected due to the unrecognised warning Wfoo. However, by running

ghc -Werror=unrecognised-warning-flags -Werror=foo Main.hs

I only got a warning instead of a compilation error.

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