all: release v0.25.0 (#493)

This commit will be tagged v0.25.0.

CHANGES.md

@@ -1,3 +1,32 @@
+# v0.25.0
+
+## Announcements
+
+[goolgeapis/google-api-go-client](https://github.com/googleapis/google-api-go-client)
+has moved its source of truth to GitHub and is no longer a mirror. This means
+that our contributing process has changed a bit. We will now be conducting all
+code reviews on GitHub which means we now accept Pull Requests! If you have a
+version of the codebase previously checked out you may wish to update your git
+remote to point to GitHub.
+
+## Changes
+
+- all:
+  - Updated instructions in CONTRIBUTING.md for pull requests.
+- idtoken:
+  - Validate now checks to see if the token is expired.
+- sheets:
+  - Update ExtendedValue Fields to be pointer types.
+- support/bunder:
+  - Fix a deadlock that could when handler limit was set to one.
+- transport:
+  - Allow `GOOGLE_API_USE_MTLS` overriding the mTLS endpoint behavior for the
+    HTTP client.
+- Various updates to autogenerated clients.
+
+_Please note:_ the release version is not indicative of an individual client's
+stability or version.
+
 # v0.24.0
 
 ## Changes