Revert reverting package installation during CI

This reverts commit 790afef so that the
code can be merged back into dev, once issue #589 is fixed.

.github/workflows/ci.yaml

@@ -52,3 +52,7 @@ jobs:
         run: "python -m nox -s build"
         env:
           PLATFORM: ${{ matrix.os.image }}
+      - name: "Install the package"
+        run: "python -m nox -s install"
+        env:
+          PLATFORM: ${{ matrix.os.image }}

noxfile.py

@@ -1,3 +1,4 @@
+from pathlib import Path
 from pprint import pformat
 
 import nox
@@ -58,3 +59,11 @@ def build(session):
     session.install("twine")
     session.run("python", "setup.py", "bdist", "bdist_wheel")
     session.run("twine", "check", "dist/eTraGo*")
+
+
+@nox.session(python=["3", "3.8", "3.9", "3.10", "3.11"])
+def install(session):
+    """Install the package."""
+    setdefaults(session)
+    session.run("python", "-mpip", "install", "--upgrade", "pip")
+    session.run("python", "-mpip", "install", *Path("dist").glob("*.whl"))