ci: run a simple build matrix first

.github/workflows/main.yml

@@ -11,6 +11,33 @@ on:
 jobs:
   run:
     name: Build
+    strategy:
+      fail-fast: true
+      matrix:
+        os:
+            - ubuntu-latest
+        ocaml-compiler:
+            - '4.03.x'
+            - '4.06.x'
+            - '4.07.x'
+            - '4.08.x'
+            - '4.13.x'
+
+    runs-on: ${{ matrix.os }}
+    steps:
+      - uses: actions/checkout@v2
+      - name: Use OCaml ${{ matrix.ocaml-compiler }}
+        uses: ocaml/setup-ocaml@v2
+        with:
+          ocaml-compiler: ${{ matrix.ocaml-compiler }}
+
+      - run: opam pin -n .
+      - run: opam depext -y containers containers-data containers-thread
+      - run: opam install containers containers-data containers-thread --deps-only
+      - run: opam exec -- dune build '@install'
+
+  run:
+    name: Build and test
     strategy:
       fail-fast: false
       matrix:
@@ -20,7 +47,6 @@ jobs:
             - windows-latest
         ocaml-compiler:
             - '4.03.x'
-            - '4.08.x'
             - '4.13.x'
 
     runs-on: ${{ matrix.os }}