rm python pin in both workflows

Author: cadenmyers13

.github/workflows/matrix-and-codecov-on-merge-to-main.yml

@@ -17,7 +17,6 @@ jobs:
       project: diffpy.cmi
       c_extension: false
       headless: false
-      python_versions: "3.12, 3.13"
       run: |
         set -Eeuo pipefail
         echo "Test cmds"

.github/workflows/tests-on-pr.yml

@@ -11,7 +11,6 @@ jobs:
       project: diffpy.cmi
       c_extension: false
       headless: false
-      python_version: 3.13
       run: |
         set -Eeuo pipefail
         echo "Test cmds"