fix(typo): Fix typo in CDC DFU flash tutorial (#10584)

* Update cdc_dfu_flash.rst

* Update docs/en/tutorials/cdc_dfu_flash.rst

Co-authored-by: Jan Procházka <90197375+P-R-O-C-H-Y@users.noreply.github.com>

* Update docs/en/tutorials/cdc_dfu_flash.rst

Co-authored-by: Lucas Saavedra Vaz <32426024+lucasssvaz@users.noreply.github.com>

---------

Co-authored-by: Jan Procházka <90197375+P-R-O-C-H-Y@users.noreply.github.com>
Co-authored-by: Lucas Saavedra Vaz <32426024+lucasssvaz@users.noreply.github.com>

Author: 3 people

docs/en/tutorials/cdc_dfu_flash.rst

@@ -66,8 +66,8 @@ Go to the Tools menu in the Arduino IDE and set the following options:
 
 * USB DFU On Boot -> Enabled
 
-Setp 3 - Flash
-^^^^^^^^^^^^^^
+3. Flash
+^^^^^^^^
 
 Now you can upload your sketch to the device. After flashing, you need to manually reset the device.