Update Core changelog for M71 (#5597)

* Update Core changelog for M71

* Used issue number, not PR number.

Author: ryanwilson

FirebaseCore/CHANGELOG.md

@@ -1,3 +1,7 @@
+# v6.7.1 -- M71
+- [fixed] Fixed `FirebaseApp`s `bundleID` verification, allowing exact `bundleID` matches
+  for extensions. (#5126)
+
 # v6.7.0 -- M70
 - [fixed] Updated nanopb to 0.3.9.5 (across all Firebase pods). This includes a fix for
   [CVE-2020-5235](https://github.com/nanopb/nanopb/security/advisories/GHSA-gcx3-7m76-287p).