[ci] Use python 3.11 for signing tasks

[pjcollins]

Authenticode signing attempts started failing recently with:

ERROR: 'xsign' is misspelled or not recognized by the system.

Updating to Python 3.11 is the suggested fix for this issue.

[pjcollins]

Testing this with https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=8832765&view=results

[jonpryor]

Good news, bad news, etc.

Yay, it builds!

Unfortunately, InstallAndroidDependenciesTest() fails; install-deps.log mentions:

Task "InstallAndroidDependencies" (TaskId:7)
  Task Parameter:ManifestType=GoogleV2 (TaskId:7)
  Task Parameter:AcceptAndroidSDKLicenses=True (TaskId:7)
  Task Parameter:TimeoutInMinutes=7 (TaskId:7)
  Task Parameter:AndroidSdkPath=/Users/runner/work/1/a/TestRelease/12-19_22.45.06/temp/InstallAndroidDependenciesTest/android-sdk (TaskId:7)
  Task Parameter:
      Dependencies=
          platforms/android-33
          build-tools/32.0.0
                  Version=32.0.0
          platform-tools
                  Version=34.0.4
          cmdline-tools/7.0
                  Version=7.0 (TaskId:7)
…
  Component Android SDK Platform-Tools r34.0.5 not present on the system  (TaskId:7)
…
  /Library/Frameworks/Mono.framework/External/xbuild/Xamarin/Android/Xamarin.Installer.Common.targets(12,3): warning : Dependency `platform-tools` should have been installed but could not be resolved. You can attempt to install it with: `/Users/runner/work/1/a/TestRelease/12-19_22.45.06/temp/InstallAndroidDependenciesTest/android-sdk/cmdline-tools/7.0/bin/sdkmanager --install "platform-tools"` [/Users/runner/work/1/a/TestRelease/12-19_22.45.06/temp/InstallAndroidDependenciesTest/UnnamedProject.csproj]

InstallAndroidDependencies() specifies the GoogleV2 manifest, not the Xamarin manifest:

https://github.com/xamarin/xamarin-android/blob/d17-5/src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/AndroidDependenciesTests.cs#L43

The Google Manifest at https://dl.google.com/android/repository/repository2-3.xml no longer contains platform-tools 34.0.4, but only 34.0.5. (Comments within the manifest suggest this happened on or after 2023-Oct-5.)

Guess we'll need to bump that value. :-/