minor #153 Setup PHP and use PHP 7.4 (Nyholm)

This PR was merged into the master branch.

Discussion
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Setup PHP and use PHP 7.4

Here is the failing job: https://github.com/carsonbot/carsonbot/actions/runs/466322348

Commits
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b484d86 Setup PHP and use PHP 7.4

Author: weaverryan

.github/workflows/find-reviewer.yml

@@ -10,6 +10,12 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
+      - name: Set up PHP
+        uses: shivammathur/setup-php@2.7.0
+        with:
+          php-version: 7.4
+          coverage: none
+
       - name: Checkout code
         uses: actions/checkout@v2