[ci] Changes to fix CI.

[jpobst]

Author's note: I know very little about Cake or this repository's CI, so please review thoroughly! 😁

Changes to fix the currently broken XC CI:

• Updating Cake had a breaking change that no longer allows empty CLI arguments to be passed with --foo="". It is now required to omit the equals sign.

• Errors when trying to run build-manifest.cake fixed by removing methods 🤷‍♂️:

C:/code/XamarinComponents/.ci/build-manifest.cake(421,6): error CS0111: Type 'Submission#0' already defines a member called 'IsRunningOnMacOs' with the same parameter types
C:/code/XamarinComponents/.ci/build-manifest.cake(425,6): error CS0111: Type 'Submission#0' already defines a member called 'IsRunningOnLinux' with the same parameter types

• Error when trying to run build-manifest.cake fixed by updating Cake.XCode:

C:/code/XamarinComponents/.ci/build-manifest.cake(234,4): error CS0103: The name 'CocoaPodRepoUpdate' does not exist in the current context

• Revert requested XCode to 13.2.1. We are building on macos-11, which does not support XCode 13.3.1.

Note this PR will show as failed because CI is set up to use the .ci files from main. Here is a build that actually uses the files from the PR: https://devdiv.visualstudio.com/DevDiv/_build/results?buildId=6282119.