InternPool: fix dbHelper after 4976b58

You must now write '_ = &f' rather than just '_ = f' to ensure a
function is compiled into a binary.

src/InternPool.zig

@@ -1498,7 +1498,7 @@ pub const Index = enum(u32) {
 
     comptime {
         if (builtin.mode == .Debug) {
-            _ = dbHelper;
+            _ = &dbHelper;
         }
     }
 };