Set default Python version in CI/CD

- Set appveyor's default python version
- Removes packages that are already pre-installed

appveyor.yml

@@ -11,16 +11,16 @@ cache:
 # Only build on tags
 skip_non_tags: true
 
-install:
-  - sudo apt-get update
-  - sudo apt-get install -y build-essential make msitools wget unzip python3 python3-dev python3-pip git p7zip-full golang-go aria2
+init:
+  - export PATH=/home/appveyor/venv3.11/bin:$PATH
 
-build_script:
+install:
+  - sudo apt-get install -y msitools aria2
   - make setup-minimal
   - make mozbootstrap
   - mkdir -p dist
 
-test_script:
+build_script:
   - python3 ./multibuild.py --target windows macos linux --arch x86_64
 
 artifacts: