Add post-release install tests

Author: dflook

.github/workflows/release.yaml

@@ -45,3 +45,62 @@ jobs:
             Update docs
 
             [skip ci]
+
+  test_package:
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        python: [2.7, 3.4, 3.5, 3.6, 3.7, 3.8]
+    needs: [release]
+    container:
+      image: danielflook/python-minifier-build:fedora30-2020-05-03
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+
+      - name: Install package
+        run: |
+          if [[ "${{ matrix.python }}" == "2.7" || "${{ matrix.python }}" == "3.7" ]]; then
+             echo "pip is already installed"
+          elif [[ "${{ matrix.python }}" == "3.8" ]]; then
+             curl https://bootstrap.pypa.io/get-pip.py | python${{ matrix.python }}
+          else
+             curl https://bootstrap.pypa.io/pip/${{ matrix.python }}/get-pip.py | python${{ matrix.python }}       
+          fi
+
+          pip${{ matrix.python }} install python-minifier==${{ github.event.release.tag_name }}
+          pyminify --version
+
+  test_package_3_3:
+    runs-on: ubuntu-latest
+    needs: [release]
+    container:
+      image: danielflook/python-minifier-build:fedora28-2020-05-03
+    steps:
+      - name: Install package
+        run: |
+          curl https://bootstrap.pypa.io/pip/3.3/get-pip.py | python3.3
+          pip3.3 install python-minifier==${{ github.event.release.tag_name }}
+          pyminify --version
+
+  test_package_3_9:
+    runs-on: ubuntu-latest
+    needs: [release]
+    container:
+      image: danielflook/python-minifier-build:fedora32-2020-10-11
+    steps:
+      - name: Install package
+        run: |
+          pip3.9 install python-minifier==${{ github.event.release.tag_name }}
+          pyminify --version
+
+  test_package_3_10:
+    runs-on: ubuntu-latest
+    needs: [release]
+    container:
+      image: danielflook/python-minifier-build:fedora34-2021-10-05
+    steps:
+      - name: Install package
+        run: |
+          pip3.10 install python-minifier==${{ github.event.release.tag_name }}
+          pyminify --version