build: don't check for deprecated qt5 package

Use qt@5 instead.

configure.ac

@@ -694,8 +694,8 @@ case $host in
            export PKG_CONFIG_PATH="$($BREW --prefix sqlite3 2>/dev/null)/lib/pkgconfig:$PKG_CONFIG_PATH"
          fi
 
-         if $BREW list --versions qt5 >/dev/null; then
+         if $BREW list --versions qt@5 >/dev/null; then
-           export PKG_CONFIG_PATH="$($BREW --prefix qt5 2>/dev/null)/lib/pkgconfig:$PKG_CONFIG_PATH"
+           export PKG_CONFIG_PATH="$($BREW --prefix qt@5 2>/dev/null)/lib/pkgconfig:$PKG_CONFIG_PATH"
          fi
 
          case $host in