Fixed typo and added unregister to spelling_wordlist

Signed-off-by: Zakaria Talbi Lalmi <zakariatalbi@eprosima.com>

Author: ZakariaTalbi

docs/rst/spelling_wordlist.txt

@@ -43,6 +43,7 @@ Requiredness
 runtime
 scalable
 Tsan
+unregister
 utils
 validator
 Vulcanexus

docs/rst/user_manual/participants/xml.rst

@@ -127,7 +127,7 @@ Overriding profile QoS from the YAML configuration
 
 When a matching XML profile is applied, the QoS fields explicitly set by the user in the YAML
 configuration take precedence over the values in the XML profile.
-This behaviour is controlled by the ``endpoint-qos-mode`` participant tag, which accepts two values:
+This behavior is controlled by the ``endpoint-qos-mode`` participant tag, which accepts two values:
 
 * ``xml-overridable`` *(default)*: the XML profile is applied first, and any QoS field explicitly set in
   the YAML configuration overrides the corresponding value from the profile.