CI: Test ArduinoJson's configuration

extras/conf_test/x64.cpp

@@ -0,0 +1,15 @@
+#include <ArduinoJson.h>
+
+static_assert(ARDUINOJSON_USE_LONG_LONG == 1, "ARDUINOJSON_USE_LONG_LONG");
+
+static_assert(ARDUINOJSON_SLOT_OFFSET_SIZE == 4,
+              "ARDUINOJSON_SLOT_OFFSET_SIZE");
+
+static_assert(ARDUINOJSON_LITTLE_ENDIAN == 1, "ARDUINOJSON_LITTLE_ENDIAN");
+
+static_assert(ARDUINOJSON_USE_DOUBLE == 1, "ARDUINOJSON_USE_DOUBLE");
+
+static_assert(sizeof(ARDUINOJSON_NAMESPACE::VariantSlot) == 32,
+              "sizeof(VariantSlot)");
+
+int main() {}