Define python dependency range as a matrix fallback. (#1409)

This PR moves the definition of `python>=3.9,<3.11` into the `py_version` dependency list, under the empty (fallback) matrix. This change aligns RMM's `dependencies.yaml` with other RAPIDS repositories.

Authors:
  - Bradley Dice (https://github.com/bdice)

Approvers:
  - Vyas Ramasubramani (https://github.com/vyasr)
  - Ray Douglass (https://github.com/raydouglass)

URL: #1409

Author: bdice

dependencies.yaml

@@ -11,6 +11,7 @@ files:
       - cudatoolkit
       - develop
       - docs
+      - py_version
       - run
       - test_python
   test_python:
@@ -72,7 +73,6 @@ dependencies:
           - fmt>=10.1.1,<11
           - scikit-build-core>=0.7.0
           - spdlog>=1.12.0,<1.13
-          - python>=3.9,<3.11
       - output_types: [requirements, pyproject]
         packages:
           - scikit-build-core[pyproject]>=0.7.0
@@ -195,6 +195,9 @@ dependencies:
               py: "3.10"
             packages:
               - python=3.10
+          - matrix:
+            packages:
+              - python>=3.9,<3.11
   run:
     common:
       - output_types: [conda, requirements, pyproject]