[PRISM] Fix a -Wformat-zero-length warning

../prism_compile.c: In function ‘pm_compile_node’:
../prism_compile.c:2330:20: warning: zero-length gnu_printf format string [-Wformat-zero-length]
 2330 |             rb_bug("");
      |                    ^~

prism_compile.c

@@ -2327,7 +2327,7 @@ pm_compile_node(rb_iseq_t *iseq, const pm_node_t *node, LINK_ANCHOR *const ret,
                 return;
             }
             COMPILE_ERROR(ERROR_ARGS "Invalid break");
-            rb_bug("");
+            rb_bug("Invalid break");
         }
         return;
       }