How can I tell Gatekeeper not to check (downloaded) files with a specific extension?

Since the upgrade to macOS 15.4, I've noticed that every time I try to open a [Lilypond](https://lilypond.org/) file, Gatekeeper blocks me from doing so: > Apple could not verify "EL 38 1.ly" is free of malware that may harm your Mac or compromise your privacy. Thanks to e.g. [this answer](https://discussions.apple.com/thread/255852595?answerId=260941200022&sortBy=rank#260941200022) I know I can fix this via System Settings → Privacy & Security and scrolling down to the Security area. However, I have to do that every time I open a new Lilypond file, which is rather annoying. Is there a way I can tell Gatekeeper to ignore files with the .ly extension? I have already set BBEdit as the default app to open .ly files. Right-clicking the file and choosing Open With → BBEdit.app gives the same dialog. ls gives the following information:

% ls -@l ~/Downloads/EL21.ly
-rw-r--r--@ 1 Glorfindel  staff  3314 May 11 20:08 /Users/Glorfindel/Downloads/EL21.ly
	com.apple.metadata:kMDItemWhereFroms	 181 
	com.apple.quarantine	  57

If I then do

cat EL21.ly > test.ly

the test.ly file opens without problems, so it seems related to the file being downloaded.