submodules: update cargo from 974eb438d to 2d5c2381e

Changes:
````
Use the same index location on nightly as beta
relax deprecated diagnostic message check
Don't print to raw stderr in test
Emit the `test` field in cargo metadata
````

diff --git a/src/tools/cargo b/src/tools/cargo
index 974eb438da8ced6e3becda2bbf63d9b643eacdeb..2d5c2381e4e50484bf281fc1bfe19743aa9eb37a 160000 (submodule)
--- a/src/tools/cargo
+++ b/src/tools/cargo
@@ -1 +1 @@
-Subproject commit 974eb438da8ced6e3becda2bbf63d9b643eacdeb
+Subproject commit 2d5c2381e4e50484bf281fc1bfe19743aa9eb37a