Fix Travis Composer config

.travis.yml

@@ -29,14 +29,16 @@ before_install:
   # turn off XDebug
   - phpenv config-rm xdebug.ini || return
 
+  # Temp downgrade Composer to v1 (see https://github.com/mautic/mautic/pull/9315 for details)
+  - composer self-update --1
+
   # install dependencies in parallel
   - travis_retry composer global require hirak/prestissimo
 
   # set to test environment for Symfony's commands in post install commands
   - export SYMFONY_ENV="test"
 
 install:
-  - composer self-update --1
   - composer install
 
   # Clobber is needed because PCOV normally only works with PHPUnit 8+. Needed only to run test coverage.