chore(deps): update Symbol collector CLI to v1.21.0 (#2196)

Co-authored-by: GitHub <[email protected]>

Author: github-actions[bot]

scripts/flutter_symbol_collector/lib/src/symbol_collector_cli.dart

@@ -19,7 +19,7 @@ class SymbolCollectorCli {
 
   // https://github.com/getsentry/symbol-collector/releases
   @internal
-  static const version = '1.19.0';
+  static const version = '1.21.0';
 
   @internal
   late final String cli;