(chore) Update invite-accept email (#13790)

There's outdated text leftover from previous changes

src/sentry/templates/sentry/accept-organization-invite.html

@@ -16,7 +16,7 @@
         </div>
 
         <p style="font-size: 1.3em;">
-          {% blocktrans %}<strong>{{ org_name }}</strong> is using Sentry to aggregate errors.{% endblocktrans %}
+          {% blocktrans %}<strong>{{ org_name }}</strong> is using Sentry to track and debug errors.{% endblocktrans %}
         </p>
 
         {% if existing_member %}

src/sentry/templates/sentry/emails/member-invite.txt

@@ -1,9 +1,9 @@
-Welcome to Sentry
+You've been invited to Sentry
 
-Your teammates over at {{ organization.name }} have already been using Sentry without you, but the good news is that you've been invited to join them.
+Your teammates at {{ organization.name }} are using Sentry to track and debug software errors.
 
 Join your team by visiting the following url:
 
     {{ url }}
 
-If you'd like to learn more about Sentry before diving head-first, check out our website, https://sentry.io/
+Check out the Sentry website (https://sentry.io) if you'd like to learn more before diving in.

tests/fixtures/emails/invitation.txt

@@ -1,9 +1,9 @@
-Welcome to Sentry
+You've been invited to Sentry
 
-Your teammates over at Example have already been using Sentry without you, but the good news is that you've been invited to join them.
+Your teammates at Example are using Sentry to track and debug software errors.
 
 Join your team by visiting the following url:
 
     http://testserver/accept/1/None/
 
-If you'd like to learn more about Sentry before diving head-first, check out our website, https://sentry.io/
+Check out the Sentry website (https://sentry.io) if you'd like to learn more before diving in.