Install PostgreSQL ourselves in macOS CI workflow

It used to be part of macos-12 image but is not present in the later
ones for whatever reason.

Installing postgresql formula using brew already initializes the
database cluster but does it in a non-default directory, so adjust
PGDATA definition accordingly and remove "pg_ctl init" which is not
needed any longer.

.github/workflows/ci.yml

@@ -116,7 +116,7 @@ jobs:
               ;;
 
             macOS)
-              set_env_var PGDATA /usr/local/var/postgres
+              set_env_var PGDATA /opt/homebrew/var/postgresql@14
               ;;
           esac
 
@@ -141,8 +141,7 @@ jobs:
             set_env_var BUILD_EXAMPLES YES
           fi
 
-      - name: Install dependencies under Linux
-        if: runner.os == 'Linux'
+      - name: Install dependencies
         run: ./scripts/ci/install.sh
 
       - name: Prepare for build

scripts/ci/before_build_postgresql.sh

@@ -13,7 +13,6 @@ case "$(uname)" in
         ;;
 
     Darwin)
-        pg_ctl init
         pg_ctl start
         pg_isready --timeout=60
         createuser --superuser postgres

scripts/ci/install.sh

@@ -52,6 +52,19 @@ case "$(uname)" in
     FreeBSD)
         pkg install -q -y bash cmake
         ;;
+
+    Darwin)
+        case "${SOCI_CI_BACKEND}" in
+            postgresql)
+                brew install postgresql
+                ;;
+        esac
+        ;;
+
+    *)
+        echo "Unknown platform: $(uname)"
+        exit 1
+        ;;
 esac
 
 install_script="${SOCI_SOURCE_DIR}/scripts/ci/install_${SOCI_CI_BACKEND}.sh"