test: move assembler-tests into ./test/run/

Move the last remaining test into the correct subdir. With this done,
all our tests run in one of the 3 groups:

   * `make test-src`
     Run tests against the source-code, including linters.

   * `make test-mod`
     Run unit-tests on the individual python modules. This needs no
     special permissions (unless noted in each test) or runtime
     environments. It is meant to be fast and easy to run in all
     circumstances.

   * `make test-run`
     Run tests that execute the osbuild pipeline. This requires
     superuser privileges and will likely take a while. Furthermore,
     this might produce large artifacts.

.github/workflows/runtime-tests.yml

@@ -1,37 +0,0 @@
-name: Runtime Tests
-
-on: [pull_request, push]
-
-#
-# We set `PYTHONUNBUFFERED` to get more immediate and ordered output from
-# python programs. This should not be necessary if all relevant output used the
-# unbuffered stderr, but that is not entirely under our control.
-#
-env:
-  PYTHONUNBUFFERED: 1
-
-jobs:
-  assembler_tests:
-    name: "Assembler Tests"
-    runs-on: ubuntu-latest
-    steps:
-    - name: "Clone Repository"
-      uses: actions/checkout@v2
-    - name: "Install Dependencies"
-      run: |
-        sudo apt-get update
-        sudo apt-get -y install \
-          nbd-client \
-          qemu-utils \
-          rpm \
-          systemd-container \
-          tar \
-          yum
-    - name: "Set up Python"
-      uses: actions/setup-python@v1
-      with:
-        python-version: 3.7
-    - name: Install Python Packages
-      run: pip install jsonschema
-    - name: "Run Assembler Tests"
-      run: sudo env "PATH=$PATH" python3 -m unittest -v test.test_assemblers