ci: Test on Python 3.13 alpha

.github/workflows/test.yml

@@ -15,7 +15,11 @@ jobs:
     strategy:
       matrix:
         include:
-          - python-version: "3.12.0-alpha.7"
+          - python-version: "3.13.0-alpha.6"
+            with-opt-deps: false  # https://github.com/pyca/cryptography/issues/10806
+            runs-on: ubuntu-22.04
+
+          - python-version: "3.12.0"
             with-opt-deps: true
             runs-on: ubuntu-22.04
 
@@ -67,7 +71,7 @@ jobs:
 
       - name: Upgrade pip
         run: |
-          python3 -m pip install --upgrade pip
+          python3 -m pip install --upgrade pip setuptools
 
       - name: Install optional dependencies
         if: ${{ matrix.with-opt-deps }}

setup.py

@@ -49,10 +49,12 @@ except ImportError:
     install. This package is pretty standard, and often installed alongside
     Python, but it is missing on your system.
     Try installing it with your package manager, it is usually called
-    'python3-setuptools'. If that does not work, try installing python3-pip
+    'python3-setuptools'; or with '%s -m pip install setuptools'.
+    If that does not work, try installing python3-pip
     instead, either with your package manager or by following these
     instructions: https://pip.pypa.io/en/stable/installation/ (replace
-    'python' with 'python3' in all the commands)""")
+    'python' with 'python3' in all the commands)"""
+    % sys.executable)
     sys.stderr.write(os.linesep*2)
     sys.stderr.write(textwrap.fill(s))
     sys.stderr.write(os.linesep*2)