Notifications are sent if user posts a comment referring their own proposal/idea/etc.

**Describe the bug**
When the user refers their own content from a comment, they are notified by email. I think this is redundant, why do I need to know I just created a comment myself that referred my own proposal?

**To Reproduce**

1. Create a proposal
2. Grab a link to that proposal
3. Create another proposal
4. Go to the another proposal
5. Create a comment that refers to the first proposal (add the link to the first proposal to the comment)
6. Wait a bit
7. Receive an email that "someone" just mentioned my proposal

**Expected behavior**
I would not expect to get notified about what I just did myself.

**Extra data**

• Device: (any)
• Device OS: (any)
• Browser: (any)
• Decidim Version: e.g. 0.25, 0.26, ... (the version at MetaDecidim)
• Decidim installation: e.g. MetaDecidim