ENH: Update Azure CI Python version from 3.9 to 3.10

ITK v6.0 requires Python >= 3.10 for wrapping. Update the
LinuxCxx20 CI job to use Python 3.10 instead of 3.9.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hjmjohnson

Testing/ContinuousIntegration/AzurePipelinesLinux.yml

@@ -245,7 +245,7 @@ jobs:
       displayName: "Checkout pull request HEAD"
     - task: UsePythonVersion@0
       inputs:
-        versionSpec: "3.9"
+        versionSpec: "3.10"
         architecture: "x64"
     - bash: |
         set -x