Correct poetry install flag format in GitHub Actions workflow

Previously, the `poetry install` command was using a space instead of an equals sign for the `--with` flag. This commit corrects it by changing `--with testing` to `--with=testing`, ensuring the installation command is properly recognized and executed.

.github/workflows/test-suite.yml

@@ -46,9 +46,8 @@ jobs:
           virtualenvs-create: true
           virtualenvs-in-project: true
           installer-parallel: true
-          installation-arguments: --with=testing
       - name: Install dependencies
-        run: poetry install --no-interaction --with testing
+        run: poetry install --no-interaction --with=testing
       - name: Run PyTest with coverage
         env:
           GH_TOKEN: ${{ steps.generate-token.outputs.token }}