Use develop in CI when possible

.github/workflows/testing.yml

@@ -5,8 +5,12 @@ jobs:
   unix-testing:
     strategy:
       matrix:
-        os: [ubuntu-16.04, ubuntu-18.04, macos-10.15]
+        os: [ubuntu-18.04, ubuntu-16.04, macos-10.15]
         cc: [gcc, clang]
+        include:
+          - os: ubuntu-18.04
+            cc: gcc
+            target: develop
     runs-on: ${{ matrix.os }}
     steps:
       - uses: actions/checkout@v2
@@ -16,7 +20,7 @@ jobs:
           ./.github/actions/install_deps.sh ${{ matrix.os }}
       - name: Build
         run: |
-          make -j Q= CC=${{ matrix.cc }}
+          make ${{ matrix.target }} -j Q= CC=${{ matrix.cc }}
       - name: Install
         run: |
           sudo make install -j Q=