diff --git a/.github/workflows/pull-request.yml b/.github/workflows/pull-request.yml
index 45ebb97..03d840c 100644
--- a/.github/workflows/pull-request.yml
+++ b/.github/workflows/pull-request.yml
@@ -71,7 +71,6 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        operating-system: [ ubuntu-20.04 ]
         version: ['~4.2.0', '~4.3.0', '~4.4.0', '^4.5']
     steps:
       - name: Checkout