The source project of this merge request has been removed.
avoid recompressing expected PNGs (LP: #1918445)
In Ubuntu pkgstripfiles calls optipng which often works fine to save
data, but in the case of openscad-testing-data the recompression
breaks the later comparison of those in e.g. autopkgtests.
For Debian this should be a no-op, but accepting it would be helpful for Ubuntu as a downstream.