chore(php): remove "no check-in" protobuf header

Google APIs · copybara-github · commit d252e591a655 · 2026-03-12T13:37:17.000-07:00
PiperOrigin-RevId: 882754677
diff --git a/generator-versions.json b/generator-versions.json
@@ -15,7 +15,7 @@
     "sha": null
   },
   "php": {
-    "version": "1.20.4",
+    "version": "1.21.0",
     "commit": null,
     "sha": null
   },
