Move clippy cfg_attr for bigdecimal to function scope

Author: kestred

diesel/src/pg/types/numeric.rs

@@ -1,8 +1,5 @@
 #[cfg(feature = "bigdecimal")]
 mod bigdecimal {
-    // NOTE: No `std::ops::MulAssign` impl for `BigInt`
-    #![cfg_attr(feature = "cargo-clippy", allow(assign_op_pattern))]
-
     extern crate bigdecimal;
     extern crate num_bigint;
     extern crate num_integer;
@@ -90,6 +87,8 @@ mod bigdecimal {
     }
 
     impl<'a> From<&'a BigDecimal> for PgNumeric {
+        // NOTE(clippy): No `std::ops::MulAssign` impl for `BigInt`
+        #[cfg_attr(feature = "cargo-clippy", allow(assign_op_pattern))]
         fn from(decimal: &'a BigDecimal) -> Self {
             let (mut integer, scale) = decimal.as_bigint_and_exponent();
             let scale = scale as u16;