use ubuntu1804

Author: p

.evergreen/config/standard.yml.erb

@@ -478,7 +478,7 @@ buildvariants:
       mongodb-version: ['4.4']
       os: ubuntu1804
       fle: fle
-      docker-distro: debian10
+      docker-distro: ubuntu1804
     display_name: "FLE: ${mongodb-version} ${ruby}"
     tasks:
       - name: "test-fle-via-docker"