chore(main): release auth 0.16.4 (googleapis#12667)

Author: release-please[bot]

.release-please-manifest-individual.json

@@ -1,5 +1,5 @@
 {
-  "auth": "0.16.3",
+  "auth": "0.16.4",
   "auth/oauth2adapt": "0.2.8",
   "bigquery": "1.69.0",
   "bigquery/v2": "0.0.0",

auth/CHANGES.md

@@ -1,5 +1,12 @@
 # Changelog
 
+## [0.16.4](https://github.com/googleapis/google-cloud-go/compare/auth/v0.16.3...auth/v0.16.4) (2025-08-06)
+
+
+### Bug Fixes
+
+* **auth:** Add UseDefaultClient: true to metadata.Options ([#12666](https://github.com/googleapis/google-cloud-go/issues/12666)) ([1482191](https://github.com/googleapis/google-cloud-go/commit/1482191e88236693efef68769752638281566766)), refs [#11078](https://github.com/googleapis/google-cloud-go/issues/11078) [#12657](https://github.com/googleapis/google-cloud-go/issues/12657)
+
 ## [0.16.3](https://github.com/googleapis/google-cloud-go/compare/auth/v0.16.2...auth/v0.16.3) (2025-07-17)