Split nightly testing from rest of CI (#309)

* Split nightly testing from rest of CI

* Single workflow allowing nightly to fail

* Fix CI

* Rename experimental into allow_failure

Author: gdalle

.github/workflows/ci.yml

@@ -13,6 +13,7 @@ jobs:
   test:
     name: Julia ${{ matrix.version }} - ${{ matrix.os }} - ${{ matrix.arch }} - ${{ github.event_name }}
     runs-on: ${{ matrix.os }}
+    continue-on-error: ${{ matrix.allow_failure }}
     strategy:
       fail-fast: false
       matrix:
@@ -26,6 +27,13 @@ jobs:
           - windows-latest
         arch:
           - x64
+        include:
+          - version: 'nightly'
+            allow_failure: true
+          - version: '1'
+            allow_failure: false
+          - version: '1.6'
+            allow_failure: false
     steps:
       - uses: actions/checkout@v2
       - uses: julia-actions/setup-julia@v1