ci: install flake8 with apt instead of pip

.github/workflows/ci.yml

@@ -30,7 +30,7 @@ jobs:
       - name: Install apt packages
         run: |
           sudo apt-get update
-          sudo apt-get install -y autoconf automake build-essential ccache cmake cpanminus gettext gperf language-pack-tr libtool-bin locales ninja-build pkg-config python3 python3-pip python3-setuptools unzip
+          sudo apt-get install -y autoconf automake build-essential ccache cmake cpanminus gettext gperf language-pack-tr libtool-bin locales ninja-build pkg-config python3 python3-pip python3-setuptools unzip flake8
 
       - name: Setup interpreter packages
         run: |

ci/install.sh

@@ -3,11 +3,6 @@
 set -e
 set -o pipefail
 
-if [[ "${CI_TARGET}" == lint ]]; then
-  python3 -m pip -q install --user --upgrade flake8
-  exit
-fi
-
 # Use default CC to avoid compilation problems when installing Python modules.
 echo "Install neovim module for Python 3."
 CC=cc python3 -m pip -q install --user --upgrade pynvim