Bump the rust version to 1.70.0 to compile ruff

Sadly needed to work around
#15939

Author: anoadragon453

flake.nix

@@ -79,7 +79,10 @@
                   # The rust toolchain and related tools.
                   # This will install the "default" profile of rust components.
                   # https://rust-lang.github.io/rustup/concepts/profiles.html
-                  (rust-bin.stable."1.60.0".default.override {
+                  #
+                  # NOTE: We currently need to set the Rust version unnecessarily high
+                  # in order to work around https://github.com/matrix-org/synapse/issues/15939
+                  (rust-bin.stable."1.70.0".default.override {
                     # Additionally install the "rust-src" extension to allow diving into the
                     # Rust source code in an IDE (rust-analyzer will also make use of it).
                     extensions = [ "rust-src" ];