Fix sample yaml for secret (#7072)

The sample yaml contains base64 encoded strings that were generated with
trailing returns. This is inconsistent to the result from the command in
which a user passes the key and value from command line. This PR removes
the trailing "Cg==" characters for consistency.

Closes: #7065

docs/tasks/inject-data-application/secret.yaml

@@ -3,5 +3,5 @@ kind: Secret
 metadata:
   name: test-secret
 data:
-  username: bXktYXBwCg==
+  username: bXktYXBw
-  password: Mzk1MjgkdmRnN0piCg==
+  password: Mzk1MjgkdmRnN0pi