Update CI.yml

Author: ChrisRackauckas

.github/workflows/CI.yml

@@ -20,6 +20,8 @@ jobs:
     steps:
       - uses: actions/checkout@v2
       - uses: julia-actions/setup-julia@v1
+        with:
+          version: ${{ matrix.version }}
       - uses: actions/cache@v1
         env:
           cache-name: cache-artifacts