CI fails on macos-arm64 only packages

Defining the pins for the mne package (added by !307 (closed)) fails on build_macos_arm_bob_devtools.

mne has different dependencies depending on the architecture, and needs pyobjc-framework-cocoa on mac machines. However, it is not found when running on a mac arm CI pipeline: package mne-1.1.0-hce30654_0 requires pyobjc-framework-cocoa, but none of the providers can be installed

• Trying to install mne directly on the mac arm machine works and mamba finds pyobjc-framework-cocoa.
• The other CI pipelines pass.

Assumption: Our CI configuration for macos arm is not correct and somehow does not search for packages on the osx-arm64 platform on conda-forge.