src: make in_makecallback() getter const

PR-URL: https://github.com/nodejs/node/pull/14697
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/env-inl.h

@@ -223,7 +223,7 @@ inline Environment::AsyncCallbackScope::~AsyncCallbackScope() {
   env_->makecallback_cntr_--;
 }
 
-inline bool Environment::AsyncCallbackScope::in_makecallback() {
+inline bool Environment::AsyncCallbackScope::in_makecallback() const {
   return env_->makecallback_cntr_ > 1;
 }
 

src/env.h

@@ -463,7 +463,7 @@ class Environment {
     AsyncCallbackScope() = delete;
     explicit AsyncCallbackScope(Environment* env);
     ~AsyncCallbackScope();
-    inline bool in_makecallback();
+    inline bool in_makecallback() const;
 
    private:
     Environment* env_;