Set the default deployment target for Macos ARM64 to 11.0.
Set the default deployment target for Macos ARM64 to 11.0.

11.0 (Big Sur) is the first version which supports ARM64 so we use
that as default.

graydon/rust,aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust