Fix dpi scaling for seexpr scripts

Now the seexpr icons should look better on high dpi displays.

Test Plan

1. Build. (Hopefully it builds just fine :) )
2. Check the result on high dpi screen (like 4k). See the seexpr script icon (I guess in the "Script" tab?). It should look nicer than before.

Formalities Checklist

• I confirmed this builds.
• I confirmed Krita ran and the relevant functions work.
• I tested the relevant unit tests and can confirm they are not broken. (If not possible, don't hesitate to ask for help!)
• I made sure my commits build individually and have good descriptions as per KDE guidelines.
• I made sure my code conforms to the standards set in the HACKING file.
• I can confirm the code is licensed and attributed appropriately, and that unattributed code is mine, as per KDE Licensing Policy.