Apply suggestions from code review

Co-authored-by: Joachim Breitner <mail@joachim-breitner.de>

Author: Kha

src/Lean/Environment.lean

@@ -924,7 +924,7 @@ def setState {σ : Type} (ext : EnvExtension σ) (env : Environment) (s : σ) :
 
 -- `unsafe` fails to infer `Nonempty` here
 private unsafe def getStateUnsafe {σ : Type} [Inhabited σ] (ext : EnvExtension σ)
-    (env : Environment) (asyncMode := ext.asyncMode) : σ :=
+    (env : Environment) (asyncMode : AsyncMode) : σ :=
   -- safety: `ext`'s constructor is private, so we can assume the entry at `ext.idx` is of type `σ`
   match asyncMode with
   | .sync     => ext.getStateImpl env.checked.get.extensions