Removed JsonVariant::as<char>() (fixes #1498)

extras/tests/FailingBuilds/variant_as_char.cpp

@@ -0,0 +1,12 @@
+// ArduinoJson - arduinojson.org
+// Copyright Benoit Blanchon 2014-2021
+// MIT License
+
+#include <ArduinoJson.h>
+
+// See issue #1498
+
+int main() {
+  DynamicJsonDocument doc(1024);
+  doc["dummy"].as<char>();
+}