I made my own that compiles Lemmy from source. Basically just make a dockerfile with a build step that git clones Lemmy, checks out the tag for the release you want, writes that version number to the rust file that needs it (see the official docker image file for this), and then do a cargo build --release.
Can't you just build it yourself, if the pull request has everything needed?
I mean, this is exactly the situation where open source excels. The "vendor" doesn't work as fast as you want, but you have all the tools to do it yourself.