fix: change pointer type to const in recursive character count function

count_char.c

@@ -28,7 +28,7 @@ int count_char_recursive(const char* str, char c) {
     }
 
     // skips the first character by moving the pointer to the next character
-    char* truncated = str + 1;
+    const char* truncated = str + 1;
 
     // true is 1, false is 0. no need to write a ternary operator
     return (str[0] == c) + count_char_recursive(truncated, c);