Use our own language-rust fork in submodule

Unfortunately, the upstream `language-rust` repo at
https://github.com/harpocrates/language-rust no longer appears to be actively
maintained, and without a fix for
harpocrates/language-rust#44, it is impossible to
build `language-rust` with GHC 9.6. This patch changes our `language-rust`
submodule to instead use our fork of `language-rust` (at
https://github.com/GaloisInc/language-rust). It is unclear if we will have to
keep doing this in the long term, but this at least unblocks us in the short
term.

Author: RyanGlScott

.gitmodules

@@ -42,7 +42,7 @@
 	url = https://github.com/galoisinc/argo
 [submodule "deps/language-rust"]
 	path = deps/language-rust
-	url = https://github.com/harpocrates/language-rust.git
+	url = https://github.com/GaloisInc/language-rust.git
 [submodule "deps/language-sally"]
 	path = deps/language-sally
 	url = https://github.com/GaloisInc/language-sally