Fix macOS CI / disable bundle generation.
Fix macOS CI / disable bundle generation.

Fix macOS CI build by removing the failing 'brew update' step and
unpinning homebrew.

Unfortunately, because of problems discovered in #12672 during the
previous attempt to fix #12657, this makes the bundle generation step
fail.

SkySkimmer/coq,gares/coq,Zimmi48/coq,SkySkimmer/coq,coq/coq,coq/coq,silene/coq,coq/coq,Zimmi48/coq,JasonGross/coq,silene/coq,JasonGross/coq,gares/coq,gares/coq,JasonGross/coq,ejgallego/coq,gares/coq,ejgallego/coq,ejgallego/coq,SkySkimmer/coq,silene/coq,SkySkimmer/coq,ejgallego/coq,Zimmi48/coq,coq/coq,gares/coq,Zimmi48/coq,JasonGross/coq