Docker image fails to build due to Centos 8 appstream being removed

[Brian Schonecker]

Perhaps switch to Rocky Linux? See #4

nfiiseed@nfiv-schon-02d:~/puppet-parser-validate-action$ docker build .
Sending build context to Docker daemon  9.728kB
Step 1/13 : FROM centos:8
 ---> 5d0da3dc9764
Step 2/13 : LABEL name="puppet-parser-validate-action"
 ---> Using cache
 ---> bc3e0eaabdf1
Step 3/13 : LABEL repository="https://github.com/irasnyd/puppet-parser-validate-action"
 ---> Using cache
 ---> d63d7d4c7569
Step 4/13 : LABEL homepage="https://github.com/irasnyd/puppet-parser-validate-action"
 ---> Using cache
 ---> b68f30955fa2
Step 5/13 : LABEL "com.github.actions.name"="puppet-parser-validate-action"
 ---> Using cache
 ---> b8ab9f9950a3
Step 6/13 : LABEL "com.github.actions.description"="GitHub Action to run 'puppet parser validate' syntax check"
 ---> Using cache
 ---> 013ca3d9fb45
Step 7/13 : LABEL "com.github.actions.icon"="share-2"
 ---> Using cache
 ---> f18b3fbfe006
Step 8/13 : LABEL "com.github.actions.color"="orange"
 ---> Using cache
 ---> ca9fa9c9ad18
Step 9/13 : LABEL "maintainer"="Ira W. Snyder <https://github.com/irasnyd/>"
 ---> Using cache
 ---> 2e0c1320018e
Step 10/13 : RUN yum -y install http://yum.puppetlabs.com/puppet7/el/8/x86_64/puppet-agent-7.11.0-1.el8.x86_64.rpm
 ---> Running in 6d78e488dd89
CentOS Linux 8 - AppStream                      479  B/s |  38  B     00:00    
Error: Failed to download metadata for repo 'appstream': Cannot prepare internal mirrorlist: No URLs in mirrorlist
The command '/bin/sh -c yum -y install http://yum.puppetlabs.com/puppet7/el/8/x86_64/puppet-agent-7.11.0-1.el8.x86_64.rpm' returned a non-zero code: 1
nfiiseed@nfiv-schon-02d:~/puppet-parser-validate-action$