Use "alice" as placeholder username instead of "john"

"alice" is normally used in combination with "bob", though.

Signed-off-by: Suguru Hirahara <acioustick@noreply.codeberg.org>

roles/custom/matrix-user-creator/vars/main.yml

@@ -18,7 +18,7 @@
 #     initial_password: some-password
 #     initial_type: admin
 #
-#   - username: john
+#   - username: alice
 #     initial_password: some-password
 #     initial_type: user
 #