Update the .gitmodules to refer to project-level tor-rust-dependencies

Closes most of #25323.

.gitmodules

@@ -1,3 +1,3 @@
 [submodule "src/ext/rust"]
 	path = src/ext/rust
-	url = https://git.torproject.org/user/sebastian/tor-rust-dependencies
+	url = https://git.torproject.org/tor-rust-dependencies

changes/ticket25323

@@ -0,0 +1,4 @@
+  o Code simplification and refactoring:
+    - Update the "rust dependencies" submodule to be an project-level
+      repository, rather than a user repository. Closes ticket 25323.
+