Pin singletons-base to 3.1
Currently, singletons-base-3.1.1
doesn't support GHC 9.2, which complicates
the GHC 9.2 build job. Let's just pin the CI to singletons-base-3.1
(which
does support 9.2) until we figure out what to do with the 9.2 job.
Currently, singletons-base-3.1.1
doesn't support GHC 9.2, which complicates
the GHC 9.2 build job. Let's just pin the CI to singletons-base-3.1
(which
does support 9.2) until we figure out what to do with the 9.2 job.