message: to_string for clippy
diff: @@ -159,17 +159,17 @@ impl<F: PrimeField + SquareRootField> CircuitGate<F> {
  /// Check if a given circuit gate is a given foreign field operation
  pub fn check_ffadd_sign(&self, sign: FFOps) -> Result<(), String> {
  if self.typ != GateType::ForeignFieldAdd {
  - return Err(format!("Gate is not a foreign field add gate"));
  + return Err("Gate is not a foreign field add gate".to_string());
  }
  match sign {
  FFOps::Add => {
  if self.coeffs[3] != F::one() {
  - return Err(format!("Gate is not performing addition"));
  + return Err("Gate is not performing addition".to_string());
  }
  }
  FFOps::Sub => {
  if self.coeffs[3] != -F::one() {
  - return Err(format!("Gate is not performing subtraction"));
  + return Err("Gate is not performing subtraction".to_string());
  }
  }
  }
  @@ -1097,7 +1097,7 @@ fn test_bad_bound() {
  index.cs.gates[2].coeffs[3] = -PallasField::two();
  assert_eq!(
  index.cs.gates[2].check_ffadd_sign(FFOps::Add),
  - Err(format!("Gate is not performing addition")),
  + Err("Gate is not performing addition".to_string()),
  );
  index.cs.gates[2].coeffs[3] = PallasField::one();
  // Modify overflow to check first the copy constraint and then the ovf constraint
  