Merge branch 'nc/csh-cp' into nc/release-12.12

Author: ncooke3

Crashlytics/CHANGELOG.md

@@ -1,3 +1,8 @@
+# 12.12.1
+- [changed] Updated `upload-symbols` to version 3.21, updated error logging in
+  `upload-symbols` and started reading the `DEVELOPER_DIR` environment
+  variable for the path to Xcode for CoreSymbolication (#15896).
+
 # 12.11.0
 - [fixed] Fixed an issue where Crashlytics API calls were silently dropped if invoked immediately after Firebase initialization.