fix: correct for surprising precedence in Bool DeMorgan laws (#4987)

The DeMorgan laws as stated were being parsed as an inequality
```lean
! ((a && b) = (!a || !b))
```
So, I added parenthesis to force the intended meaning of 
```lean
(!(a && b)) = (!a || !b)
```

Mathlib/Data/Bool/Basic.lean

@@ -304,11 +304,11 @@ theorem xor_iff_ne : ∀ {x y : Bool}, xor x y = true ↔ x ≠ y := by decide
 /-! ### De Morgan's laws for booleans-/
 
 @[simp]
-theorem not_and : ∀ a b : Bool, !(a && b) = (!a || !b) := by decide
+theorem not_and : ∀ a b : Bool, (!(a && b)) = (!a || !b) := by decide
 #align bool.bnot_band Bool.not_and
 
 @[simp]
-theorem not_or : ∀ a b : Bool, !(a || b) = (!a && !b) := by decide
+theorem not_or : ∀ a b : Bool, (!(a || b)) = (!a && !b) := by decide
 #align bool.bnot_bor Bool.not_or
 
 theorem not_inj : ∀ {a b : Bool}, !a = !b → a = b := by decide