.azurepipelines: Fix Python version (to 3.11)

Build was previously using 3.11. Using 3.12 now that is is released.
To allow scripts to take time to update, fix to 3.11.

Cc: Sean Brogan <sean.brogan@microsoft.com>
Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>
Signed-off-by: Michael Kubacki <michael.kubacki@microsoft.com>
Reviewed-by: Sean Brogan <sean.brogan@microsoft.com>

.azurepipelines/Ubuntu-PatchCheck.yml

@@ -27,7 +27,7 @@ steps:
 
 - task: UsePythonVersion@0
   inputs:
-    versionSpec: '>=3.10.6'
+    versionSpec: '3.11'
     architecture: 'x64'
 
 - script: |

.azurepipelines/templates/defaults.yml

@@ -8,5 +8,5 @@
 ##
 
 variables:
-  default_python_version: ">=3.10.6"
+  default_python_version: "3.11"
   default_linux_image: "ghcr.io/tianocore/containers/fedora-37-test:a0dd931"