Fix test bootstrap autoloader
Fix test bootstrap autoloader

The previous `require_once` statement returns `true` when it loads the
autoload file rather than an instance of `ClassLoader`. Changing the
statement to `require` returns the instance needed to add the Monolog
test directory.

pomaxa/monolog,Sgoettschkes/monolog,webwlsong/monolog,bd808/monolog,deguif/monolog,mbrevda/monolog,JeroenDeDauw/monolog,dracony/monolog,rs/monolog,nike-17/monolog,prgTW/monolog,staabm/monolog,yaoshanliang/monolog,netgusto/monolog,thiagotalma/monolog,localheinz/monolog,lyrixx/monolog,esalter/monolog,entwu/monolog,rap2hpoutre/monolog,aeryaguzov/monolog,yegortokmakov/monolog,chinaweilu/monolog,Stype/monolog,gencer/monolog,oswaldderiemaecker/monolog,peterkokot/monolog,JCook21/monolog,0x46616c6b/monolog,ehough/epilog,dailymotion/monolog,brendo/monolog,Seldaek/monolog,cherrytech/monolog,dangnguyen27/monolog,KevinMGranger/monolog,tavrij/test,supre/monolog,printerpam/monolog,vallejos/monolog