build: set resolver=2 for workspace

Our cargo actions were emitting a warning:

    warning: some crates are on edition 2021 which defaults to `resolver = "2"`, but virtual workspaces default to `resolver = "1"`
    note: to keep the current resolver, specify `workspace.resolver = "1"` in the workspace root's manifest
    note: to use the edition 2021 resolver, specify `workspace.resolver = "2"` in the workspace root's manifest

Updating the workspace's Cargo.toml to set the latest resolver version.
See related docs: https://doc.rust-lang.org/edition-guide/rust-2021/default-cargo-resolver.html

Cargo.toml

@@ -1,5 +1,8 @@
 [workspace]
 
+# Set virtual workspace's resolve to v2, to match edition 2021 crate defaults.
+resolver = "2"
+
 exclude = [
     "tools/proto-compiler",
     "tools/parameter-setup",