Apply suggestion to docs/testing_instructions.md

docs/testing_instructions.md

@@ -30,7 +30,7 @@ complete all steps.
 
 ### Logging into Nextcloud
 
-Please browse to https://files.oas.example.org and try to log in using signle
+Please browse to https://files.oas.example.org and try to log in using single
 sign-on. Use the button labeled `Login with OpenAppStack`.
 Please try logging in with your admin account and configure the email settings
 as shown in the Usage doc.