Upgrade to 3.15.0a7. (#3115)

Author: jsirois

docker/base/install_pythons.sh

@@ -17,7 +17,7 @@ DEADSNAKES_VERSIONS=(
   "3.11 {dev,venv,distutils}=3.11.15"
   "3.13 {dev,venv}=3.13.12"
   "3.14 {dev,venv}=3.14.3"
-  "3.15 {dev,venv}=3.15.0~a6"
+  "3.15 {dev,venv}=3.15.0~a7"
 )
 
 add-apt-repository --yes --ppa deadsnakes

tests/integration/venv_ITs/test_issue_1973.py

@@ -36,7 +36,7 @@ def assert_colors_import_error(
     if python.version[0] == 2:
         assert b"ImportError: No module named colors\n" in stderr, stderr.decode("utf-8")
     else:
-        assert b"ModuleNotFoundError: No module named 'colors'\n" in stderr, stderr.decode("utf-8")
+        assert b"ModuleNotFoundError: No module named 'colors'" in stderr, stderr.decode("utf-8")
 
 
 @pytest.fixture