CI: Use packages from GitHub Actions MacOS runner base-image (#1850)
openldap 2.6.8 is already installed and up-to-date.
openssl@3 3.3.1 is already installed and up-to-date.
Do not "brew install" openldap and openssl packages to avoid GitHub
Actions warnings. If GitHub stops pre-installing these packages, then
MacOS tests will fail because Squid is not compatible with MacOS's
native frameworks for LDAP and OpenSSL.