Move brew repair and update to architecture-independent script

It installs things now, so these commands are useful.

CI/before_install.macos.sh

@@ -1,5 +1,8 @@
 #!/bin/sh -ex
 
+brew tap --repair
+brew update --quiet
+
 if [[ "${MACOS_AMD64}" ]]; then
     ./CI/macos/before_install.amd64.sh
 else

CI/macos/before_install.arm64.sh

@@ -1,8 +1,5 @@
 #!/bin/sh -ex
 
-brew tap --repair
-brew update --quiet
-
 command -v qmake >/dev/null 2>&1 && qmake -v | grep -F "Using Qt version 6." >/dev/null || brew install qt@6
 
 brew install curl xquartz gd fontconfig freetype harfbuzz brotli openal-soft icu4c yaml-cpp sqlite