ci: add nvim-0.8 to version matrix

Add nvim-0.8 to version matrix of the test-nvim job.

Latest stable Neovim release is 0.9; without this change, we'd be
skipping over 0.8 during tests, potentially risking compatibility
issues.

Signed-off-by: Luca Zeuch <l-zeuch@email.de>

.github/workflows/ci.yml

@@ -59,7 +59,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        version: [v0.5.0, v0.6.0, v0.7.0, stable]
+        version: [v0.5.0, v0.6.0, v0.7.0, v0.8.0, stable]
 
     steps:
       - name: Checkout repository

.github/workflows/lint.yml

@@ -36,9 +36,13 @@ jobs:
       - name: Checkout repository
         uses: actions/checkout@v2
 
+      - name: Ensure pip is installed
+        run: |
+          apt update -y && apt install python3-pip -y
+
       - name: Install vim-vint
         run: |
-          python -m pip install --upgrade pip
+          python3 -m pip install --upgrade pip
           pip install vim-vint
 
       - name: Run VimL linter