Upgrade to 3.15.0a7.

Author: jsirois

docker/base/install_pythons.sh

@@ -17,7 +17,6 @@ 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"
 )
 
 add-apt-repository --yes --ppa deadsnakes
@@ -37,6 +36,7 @@ PYENV_VERSIONS=(
   3.5.10
   3.6.15
   3.12.13
+  3.15.0a7
   pypy2.7-7.3.20
   pypy3.5-7.0.0
   pypy3.6-7.3.3