CI: make linters emit colored output

Github Actions supports this fine, but is misdetected by flake8/mypy.
Even though pylint defaults to text instead of colorized, we might as
well do the right thing here though.

.github/workflows/lint.yml

@@ -27,7 +27,7 @@ jobs:
       with:
         python-version: '3.x'
     - run: python -m pip install pylint
-    - run: pylint mesonbuild
+    - run: pylint --output-format colorized mesonbuild
 
   flake8:
     runs-on: ubuntu-latest
@@ -37,7 +37,7 @@ jobs:
         with:
           python-version: '3.x'
       - run: python -m pip install flake8
-      - run: flake8 mesonbuild/
+      - run: flake8 --color always mesonbuild/
 
   mypy:
     runs-on: ubuntu-latest
@@ -50,3 +50,5 @@ jobs:
     - run: python run_mypy.py --allver
       env:
         PYTHONUNBUFFERED: 1
+        TERM: xterm-color
+        MYPY_FORCE_COLOR: 1