github: switch to Libera Chat

Author: emersion

.github/ISSUE_TEMPLATE/config.yml

@@ -1,5 +1,5 @@
 blank_issues_enabled: false
 contact_links:
   - name: Question
-    url: "https://webchat.freenode.net/##emersion"
-    about: "Please ask questions in ##emersion on Freenode"
+    url: "https://libera.chat/"
+    about: "Please ask questions in #emersion on Libera Chat"

.github/ISSUE_TEMPLATE/issue_template.md

@@ -7,6 +7,6 @@ about: Report a bug or request a new feature
 
 Please read the following before submitting a new issue:
 
-Do NOT create GitHub issues if you have a question about go-smtp or about the SMTP protocol in general. Ask questions on IRC in ##emersion on Freenode.
+Do NOT create GitHub issues if you have a question about go-smtp or about the SMTP protocol in general. Ask questions on IRC in #emersion on Libera Chat.
 
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