use editable install for unit tests

This appears to be a better practice than testing the code without
installing it. It also simplifies things, because dependencies are
installed automatically by pip.

Explicitly install swig as pycdio build-time dependency, even though
it is installed by default in the GitHub Ubuntu image.

.github/workflows/unit-tests.yml

@@ -2,8 +2,8 @@ name: Unit tests
 
 on:
   push:
-    branches:
-      - master
+      #branches:
+      #- master
     paths:
       - .github/workflows/unit-tests.yml
       - arver/**
@@ -40,24 +40,20 @@ jobs:
     - name: Install pycdio dependencies from distribution
       run: |
         sudo apt-get update
-        sudo apt-get install -y libcdio-dev libiso9660-dev libdiscid-dev
+        sudo apt-get install -y libcdio-dev libiso9660-dev libdiscid-dev swig
 
     - name: Install ARver dependencies from distribution
       run: |
         sudo apt-get install -y libsndfile-dev
 
-    - name: Install ARver dependencies from PyPI
+    - name: Build and install ARver
       run: |
         python3 --version
-        python3 -m pip install --upgrade pip
+        pip3 install --upgrade pip
         pip3 install setuptools
-        pip3 install -r requirements.txt
+        pip3 install --editable .
         pip3 list
 
-    - name: Build C extension
-      run: |
-        make ext
-
     - name: Run unit tests
       run: |
         make test