Update changelog and version after v2.21.6

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 See the [releases page](https://github.com/github/codeql-action/releases) for the relevant changes to the CodeQL CLI and language packs.
 
+## [UNRELEASED]
+
+No user facing changes.
+
 ## 2.21.6 - 13 Sep 2023
 
 - Better error message when there is a failure to determine the merge base of the code to analysis. [#1860](https://github.com/github/codeql-action/pull/1860)

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "codeql",
-  "version": "2.21.6",
+  "version": "2.21.7",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "codeql",
-      "version": "2.21.6",
+      "version": "2.21.7",
       "license": "MIT",
       "dependencies": {
         "@actions/artifact": "^1.1.1",

package.json

@@ -1,6 +1,6 @@
 {
   "name": "codeql",
-  "version": "2.21.6",
+  "version": "2.21.7",
   "private": true,
   "description": "CodeQL action",
   "scripts": {