**Describe the bug** When running tests of version 2.1.4 in Debian we get the following failure: ``` 1) Vips::SourceCustom can write an image to a user output stream Failure/Error: expect(image.avg).to be_within(0.001).of(109.789) expected 109.41407425505706 to be within 0.001 of 109.789 ``` This happens all the time, which makes me think if the range (`0.001`) is indeed correct. **To Reproduce** Steps to reproduce the behavior: 1. Grab the debian package for ruby-vips version 2.1.4 (latest version) 2. Try to build it. I believe if you simple try to run tests in Debian unstable you will get the same failure. Currently the default is ruby 3.1. **Expected behavior** All tests pass. **Desktop (please complete the following information):** - OS: Debian - Version: unstable (sid)