Update social.liquid: ensure social[1] is used (#2891)

Fixes #2890 

With the recent updates (v0.13.0) the email badge (social) does not
contain the email anymore.
Some link generations in social.liquid used the old schema
Also updated the handling for mastodon to be aligned to the other social
badges.

_includes/social.liquid

@@ -11,7 +11,7 @@
     {% when 'discord_id' %}
       <a href="https://discord.com/users/{{ social[1] }}" title="Discord"><i class="fa-brands fa-discord"></i></a>
     {% when 'email' %}
-      <a href="mailto:{{ site.email | encode_email }}" title="email"><i class="fa-solid fa-envelope"></i></a>
+      <a href="mailto:{{ social[1] | encode_email }}" title="email"><i class="fa-solid fa-envelope"></i></a>
     {% when 'facebook_id' %}
       <a href="https://facebook.com/{{ social[1] }}" title="Facebook"><i class="fa-brands fa-facebook"></i></a>
     {% when 'flickr_id' %}
@@ -39,7 +39,7 @@
     {% when 'linkedin_username' %}
       <a href="https://www.linkedin.com/in/{{ social[1] }}" title="LinkedIn"><i class="fa-brands fa-linkedin"></i></a>
     {% when 'mastodon_username' %}
-      <a rel="me" href="https://{{ site.mastodon_username  }}" title="Mastodon"><i class="fa-brands fa-mastodon"></i></a>
+      <a rel="me" href="https://{{ social[1] }}" title="Mastodon"><i class="fa-brands fa-mastodon"></i></a>
     {% when 'medium_username' %}
       <a href="https://medium.com/@{{ social[1] }}" title="Medium"><i class="fa-brands fa-medium"></i></a>
     {% when 'orcid_id' %}