Fix Mattermost invite link

_posts/2021/05/2021-05-19-software-policies-workshop.md

@@ -48,6 +48,6 @@ checklist for the development and introduction of a policy in the centers.
 Therefore, a communication channel is introduced.
 We encourage you to join.
 
-<a href="https://mattermost.hzdr.de/signup_user_complete/?id=hxwji435it8cxect11xr9imkoc" markdown=1>**<i class="fas fa-comments"></i> &nbsp;Click here to join the Mattermost chat.**</a>{:.btn .btn-primary}
+<a href="https://mattermost.hzdr.de/signup_user_complete/?id=t1rh7xaksbnfpb3z7d5bahym5y" markdown=1>**<i class="fas fa-comments"></i> &nbsp;Click here to join the Mattermost chat.**</a>{:.btn .btn-primary}
 
 **The Research Software Forum is looking forward to a productive exchange with you!**