Optional comment casues ICE

[Buzzec]

The comment on https://serde.rs/deserialize-struct.html# that states

// This part could also be generated independently by:
//
//    #[derive(Deserialize)]
//    #[serde(field_identifier, rename_all = "lowercase")]
//    enum Field { Secs, Nanos }

Causes an internal compiler error of thread 'rustc' has overflowed its stack fatal runtime error: stack overflow
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This is consistent with rust-lang/rust#81844.

[Buzzec]

Consistent issue was duplicate of rust-lang/rust#55779