Add test for systemwide config file support

There is now a new stage in the CICD workflow present, which will build
`bat` with the `BAT_SYSTEM_CONFIG_PREFIX` set to load the config file
from `/tests/examples/system_config/bat/config`, plus a basic set of
tests, to ensure the feature is working as expected. By default the
tests are set to ignored, as they need special setup before they can be
run.

.github/workflows/CICD.yml

@@ -96,7 +96,7 @@ jobs:
       uses: actions-rs/cargo@v1
       with:
         command: test
-        args: --locked --release -- --ignored
+        args: --locked --release --test assets -- --ignored
     - name: Syntax highlighting regression test
       run: tests/syntax-tests/regression_test.sh
     - name: List of languages
@@ -106,6 +106,32 @@ jobs:
     - name: Test custom assets
       run: tests/syntax-tests/test_custom_assets.sh
 
+  test_with_system_config:
+    name: Run tests with system wide configuration
+    runs-on: ubuntu-20.04
+    steps:
+    - name: Git checkout
+      uses: actions/checkout@v2
+    - name: Prepare environment variables
+      run: |
+        echo "BAT_SYSTEM_CONFIG_PREFIX=$GITHUB_WORKSPACE/tests/examples/system_config" >> $GITHUB_ENV
+    - name: Install Rust toolchain
+      uses: actions-rs/toolchain@v1
+      with:
+        toolchain: stable
+        default: true
+        profile: minimal
+    - name: Build and install bat
+      uses: actions-rs/cargo@v1
+      with:
+        command: install
+        args: --locked --path .
+    - name: Run unit tests
+      uses: actions-rs/cargo@v1
+      with:
+        command: test
+        args: --locked --test system_wide_config -- --ignored
+
   documentation:
     name: Documentation
     runs-on: ubuntu-20.04