s/user name/username/

Also fix tense of error message.

snikket_web/invite.py

@@ -128,7 +128,7 @@ async def register(id_: str) -> typing.Union[str, quart.Response]:
                 )
             elif exc.status == 400:
                 form.localpart.errors.append(
-                    _l("The user name was not valid")
+                    _l("The username is not valid")
                 )
             elif exc.status == 404:
                 return redirect(url_for(".view", id_=id_))

snikket_web/translations/messages.pot

@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PROJECT VERSION\n"
 "Report-Msgid-Bugs-To: EMAIL@ADDRESS\n"
-"POT-Creation-Date: 2021-01-26 16:27+0100\n"
+"POT-Creation-Date: 2021-01-26 20:49+0100\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -122,7 +122,7 @@ msgid "Registration was declined for unknown reasons"
 msgstr ""
 
 #: snikket_web/invite.py:131
-msgid "The user name was not valid"
+msgid "The username is not valid"
 msgstr ""
 
 #: snikket_web/main.py:36