Roll Fuchsia Mac SDK from SgScoXkZv... to TsvCUxpOO... (#34446)

https://dart.googlesource.com/external/github.com/flutter/engine/+/20a5cf445148fd870a095a49fd67c02d4520fc76
diff --git a/commits.json b/commits.json
index df783b3..43daeaa 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
-  "external/github.com/flutter/engine":"5d1fddcd767a8d310d7ba238c35610cab1b2c913",
+  "external/github.com/flutter/engine":"20a5cf445148fd870a095a49fd67c02d4520fc76",
   "external/github.com/flutter/flutter":"62308666d2b9bf370a4427e42df1f5f488d5f28f",
   "sdk":"2cd9404f2692d7e44d51041e42015f22e29180fe"
 }
\ No newline at end of file