chore: Prepare release 2.1.3

[fsbraun]

Summary by Sourcery

Prepare release 2.1.3 by bumping version and updating changelog

Chores:

• Bump package version to 2.1.3
• Update CHANGELOG.rst for the 2.1.3 release

[sourcery-ai]

Reviewer's Guide

This PR prepares the 2.1.3 release by updating the package version identifier and refreshing the changelog to reflect the new release.

File-Level Changes

Change	Details	Files
Bump package version to 2.1.3	Updated version constant from "2.1.2" to "2.1.3"	djangocms_frontend/__init__.py
Refresh changelog for the new release	Updated CHANGELOG.rst with the 2.1.3 release entry	CHANGELOG.rst

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[sourcery-ai]

Hey @fsbraun - I've reviewed your changes and they look great!

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.01%. Comparing base (2cb0fb5) to head (00818c1).
⚠️ Report is 27 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #292   +/-   ##
=======================================
  Coverage   89.01%   89.01%           
=======================================
  Files         124      124           
  Lines        3385     3385           
  Branches      288      288           
=======================================
  Hits         3013     3013           
  Misses        254      254           
  Partials      118      118           

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