Add Xcode 13 to available macOS VM images

[jmagman]

Xcode 13 with the iOS 15 SDK was released on Sept 20, 2021. Add it to the available macOS VM images https://cirrus-ci.org/guide/macOS/

[jmagman]

/cc @fkorotkov

[fkorotkov]

big-sur-xcode-13 is now available.

[jmagman]

@fkorotkov I tried to adopt but I'm seeing:

Parallels isolation failed: failed to create VM cloned from "big-sur-xcode-13": Parallels VM operation failed: failed to clone VM "cirrus-c69eaa5e-4187-4f9d-bad9-6b974fa09708": Parallels command returned non-zero exit code: "Failed to clone the VM: Unable to perform the operation because "big-sur-xcode-13" is in the intermediate state. Unpacking "/Users/administrator/Parallels/big-sur-xcode-13.pvmi/config.pvsp" has been started but not finished yet. Please finish unpacking."

https://github.com/flutter/plugins/pull/4429/checks?check_run_id=3889192172

[fkorotkov]

@jmagman seems it was coming from just one persistent worker. I've manually fixed the host and now it should be working. I've re-ran all three failing tasks.

[jmagman]

@jmagman seems it was coming from just one persistent worker. I've manually fixed the host and now it should be working. I've re-ran all three failing tasks.

It worked, thank you!