Fix prost documentation errors (#2093)

This PR corrects two prost documentation errors.

---------

Co-authored-by: UebelAndre <github@uebelandre.com>
diff --git a/docs/rust_proto.md b/docs/rust_proto.md
index 843c8c1..095b0ff 100644
--- a/docs/rust_proto.md
+++ b/docs/rust_proto.md
@@ -139,7 +139,7 @@
 
 toolchain(
     name = "prost_toolchain",
-    toolchain = "default_prost_toolchain_impl",
+    toolchain = "prost_toolchain_impl",
     toolchain_type = "@rules_rust//proto/prost:toolchain_type",
 )
 ```
diff --git a/docs/rust_proto.vm b/docs/rust_proto.vm
index 6bdc3b5..1fe807f 100644
--- a/docs/rust_proto.vm
+++ b/docs/rust_proto.vm
@@ -125,7 +125,7 @@
 
 toolchain(
     name = "prost_toolchain",
-    toolchain = "default_prost_toolchain_impl",
+    toolchain = "prost_toolchain_impl",
     toolchain_type = "@rules_rust//proto/prost:toolchain_type",
 )
 ```