fix: Switch to resolver v2

The published crates fail to build with an edition less than 2024
because they are packaged with `resolver = "3"`, which is a 2024-only
option. Revert back to resolver v2 to drop this requirement.

Fixes: rust-lang/compiler-builtins#883

Author: tgross35

compiler-builtins/Cargo.toml

@@ -1,5 +1,5 @@
 [workspace]
-resolver = "3"
+resolver = "2"
 members = [
     "builtins-test",
     "compiler-builtins",