Change get_completion_identifier_is_function to return a bool

A minor bugfix

modules/gdscript/gdscript_parser.cpp

@@ -8784,7 +8784,7 @@ int GDScriptParser::get_completion_argument_index() {
 	return completion_argument;
 }
 
-int GDScriptParser::get_completion_identifier_is_function() {
+bool GDScriptParser::get_completion_identifier_is_function() {
 
 	return completion_ident_is_call;
 }

modules/gdscript/gdscript_parser.h

@@ -683,7 +683,7 @@ public:
 	BlockNode *get_completion_block();
 	FunctionNode *get_completion_function();
 	int get_completion_argument_index();
-	int get_completion_identifier_is_function();
+	bool get_completion_identifier_is_function();
 
 	const List<String> &get_dependencies() const { return dependencies; }