docs: 🐛 definition of main function in c

Make the definition of `main` function compatible with ISO C
`int main()` -> `int main(void)`

docs/languages/CSharp/CSharp_1_basic.mdx

@@ -305,7 +305,7 @@ var code1 = """int i = 0;""";
 var code2 = $"""int x = {x};""";
 var code3 = $$"""
     #include <stdio.h>
-    int main() {
+    int main(void) {
         const char *s = "{y} = {{y}}";  // {y} = 2
         return 0;
     }