Run CompatHelper on Julia v1.4

CompatHelper doesn't seem to be compatible with Julia v1.5 yet.

Author: oschulz

.github/workflows/CompatHelper.yml

@@ -15,7 +15,7 @@ jobs:
     steps:
       - uses: julia-actions/setup-julia@latest
         with:
-          version: 1.5
+          version: 1.4
       - name: Pkg.add("CompatHelper")
         run: julia -e 'using Pkg; Pkg.add("CompatHelper")'
       - name: CompatHelper.main()