force v1.12 in GitHub CI (temporarily)

There are some updates in v1.12 which we should verify during the RC period.

Author: RalphAS

.github/workflows/CI.yml

@@ -29,6 +29,7 @@ jobs:
         version:
           - 'lts'
           - '1'
+          - '~1.12.0-0'
           - 'nightly'
         os:
           - ubuntu-latest

Project.toml

@@ -1,6 +1,6 @@
 name = "GenericSchur"
 uuid = "c145ed77-6b09-5dd9-b285-bf645a82121e"
-version = "0.5.5"
+version = "0.5.6-DEV"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"