CentOS through a VM - no URLs in mirrorlist

I am trying to run a CentOS 8 server through VirtualBox (6.1.30) (Vagrant), which worked just fine yesterday for me, but today I tried running a sudo yum update. I keep getting this error for some reason: [[email protected]] ~ >> sudo yum update CentOS Linux 8 - AppStream 71 B/s | 38 B 00:00 Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: No URLs in mir

[kenjiro_n]

昨年末にCentOS Linux 8のサポートが切れたことに伴いリポジトリのURLが無効になったことに対応するため CentOS Stream 8のものに切り替える方法の解説。