ensure-python: Skip "t" versions in pyenv

The recent addition of "t" version variants in CPython 3.13 has
broken the ability of jobs to assume a normal executable name.

Change-Id: Ia27bdd4e122980f65c1bb9fc28fedf43c48a5a4e

roles/ensure-python/README.rst

@@ -25,8 +25,10 @@ There are three ways to install the python interpreter:
    :type: str
 
    Optional version of python interpreter to install, such as ``3.7``.
-   Note that you should use a string value for this variable rather than
-   a float. This avoids problems with 3.10 being evaluated as 3.1.
+   Note that you should use a string value for this variable rather than a
+   float. This avoids problems with 3.10 being evaluated as 3.1. With the
+   pyenv backend it's not currently possible to select special-purpose
+   builds like the free-threading (no-GIL) variants.
 
 .. zuul:rolevar:: python_use_pyenv
    :type: bool

roles/ensure-python/tasks/pyenv.yaml

@@ -28,10 +28,13 @@
 # NOTE(mnaser): python-build does not allow us to let it install Python from a specific
 #               series so we have to do some magic to find out what's the latest
 #               release from a series
+# NOTE(fungi): due to https://github.com/pyenv/pyenv/issues/3015 we need to
+#              filter out no-GIL/free-threading "t" suffixed versions, since
+#              they don't provide the expected vanilla executables
 - name: Determine Python version
   shell: |
     set -o pipefail
-    {{ ansible_user_dir }}/.pyenv/plugins/python-build/bin/python-build --definitions | grep ^{{ python_version }} | tail -1
+    {{ ansible_user_dir }}/.pyenv/plugins/python-build/bin/python-build --definitions | grep ^{{ python_version }} | grep -v t$ | tail -1
   args:
     executable: /bin/bash
   register: _python_version