test R 4.0

Change-Id: Ia64c712bb42a6fa8e5738a6b38aa88bc4d983c81
diff --git a/.github/workflows/check-mac.yaml b/.github/workflows/check-mac.yaml
index bc278fd..8ff8cb6 100644
--- a/.github/workflows/check-mac.yaml
+++ b/.github/workflows/check-mac.yaml
@@ -12,7 +12,7 @@
       fail-fast: false
       matrix:
         config:
-        - { os: macOS-latest, r: '3.6' }
+        - { os: macOS-latest, r: '4.0' }
 
     env:
       R_REMOTES_NO_ERRORS_FROM_WARNINGS: true