Run markdown link checker only on markdown changes (#1117)

* Run markdown link checker only on markdown changes

This makes sure that this action only runs if the pull request is on the
main branch and is changing markdown files.

Fixes: https://github.com/usds/justice40-tool/issues/1114

* Remove push to main trigger

* Ignore eeoc.gov in link checker

Sometimes it seems down from the perspective of github actions.

.github/workflows/markdown-link-check.yml

@@ -1,7 +1,12 @@
 name: Check Markdown links
 on:
-  push:
   pull_request:
+    # The branches below must be a subset of the branches above
+    branches: [ main ]
+    # Run only if the pull request changes a markdown file:
+    # https://docs.github.com/en/actions/learn-github-actions/workflow-syntax-for-github-actions#onpushpull_requestpaths
+    paths:
+      - '**.md'
 jobs:
   markdown-link-check:
     runs-on: ubuntu-latest

mlc_config.json

@@ -17,6 +17,9 @@
     },
     {
       "pattern": "^https://.*medium.com"
+    },
+    {
+      "pattern": "^https://www.eeoc.gov"
     }
   ],
   "replacementPatterns": [