Add a deprecation warning for CodeQL <=2.14.5

Author: henrymercer

CHANGELOG.md

@@ -12,6 +12,12 @@ Note that the only difference between `v2` and `v3` of the CodeQL Action is the
 
   This change is currently unavailable for GitHub Enterprise Server customers, as `actions/upload-artifact@v4` and `actions/download-artifact@v4` are not yet compatible with GHES. 
 
+- _Upcoming breaking change_: Add a deprecation warning for customers using CodeQL version 2.14.5 and earlier. These versions of CodeQL were discontinued on 24 September 2024 alongside GitHub Enterprise Server 3.10, and will be unsupported by CodeQL Action versions 3.27.0 and later and versions 2.27.0 and later. [#2520](https://github.com/github/codeql-action/pull/2520)
+
+  - If you are using one of these versions, please update to CodeQL CLI version 2.14.6 or later. For instance, if you have specified a custom version of the CLI using the 'tools' input to the 'init' Action, you can remove this input to use the default version.
+
+  - Alternatively, if you want to continue using a version of the CodeQL CLI between 2.13.5 and 2.14.5, you can replace `github/codeql-action/*@v3` by `github/codeql-action/*@v3.26.11` and `github/codeql-action/*@v2` by `github/codeql-action/*@v2.26.11` in your code scanning workflow to ensure you continue using this version of the CodeQL Action.
+
 ## 3.26.10 - 30 Sep 2024
 
 - We are rolling out a feature in September/October 2024 that sets up CodeQL using a bundle compressed with [Zstandard](http://facebook.github.io/zstd/). Our aim is to improve the performance of setting up CodeQL. [#2502](https://github.com/github/codeql-action/pull/2502)