fix ci

.github/workflows/ci.yml

@@ -1,10 +1,14 @@
-on: push
+on:
+  - push
+  - pull_request
 jobs:
   test:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     name: OTP ${{matrix.otp}} / Elixir ${{matrix.elixir}}
     strategy:
+      fail-fast: false
       matrix:
+        include:
           - elixir: 1.8.2
             otp: 21.3
           - elixir: 1.9.4
@@ -21,13 +25,13 @@ jobs:
             check_format: true
     steps:
       - uses: actions/checkout@v2
-      - uses: actions/setup-elixir@v1
+      - uses: erlef/setup-elixir@v1
         with:
           otp-version: ${{matrix.otp}}
           elixir-version: ${{matrix.elixir}}
       - run: mix deps.get
       - run: mix format --check-formatted
-        if: matrix.check_formatted
-      - run: mix compile --warnings-as-errors
-        if: matrix.warnings_as_errors
+        if: ${{ matrix.check_format }}
+      - run: mix compile --force --warnings-as-errors
+        if: ${{ matrix.check_warnings }}
       - run: mix test --trace