Allow wrong_self_convention for non-Copy type

Clippy gives a warning about `wrong_self_convention` because we consume
self in a method called `is_*`. We have to consume self because the
object has a generic `E` (error type) that does not implement `Copy`.

src/blockdata/transaction.rs

@@ -503,6 +503,7 @@ impl<E> EncodeSigningDataResult<E> {
     ///     // use a hash value of "1", instead of computing the actual hash due to SIGHASH_SINGLE bug
     /// }
     /// ```
+    #[allow(clippy::wrong_self_convention)] // E is not Copy so we consume self.
     pub fn is_sighash_single_bug(self) -> Result<bool, E> {
         match self {
             EncodeSigningDataResult::SighashSingleBug => Ok(true),