Update tree-sitter-embedded-template requirement in /ruby/generator

Updates the requirements on [tree-sitter-embedded-template](https://github.com/tree-sitter/tree-sitter-embedded-template) to permit the latest version.
- [Commits](tree-sitter/tree-sitter-embedded-template@v0.20.0...v0.21.0)

---
updated-dependencies:
- dependency-name: tree-sitter-embedded-template
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

ruby/generator/Cargo.toml

@@ -11,5 +11,5 @@ clap = "4.0"
 node-types = { path = "../node-types" }
 tracing = "0.1"
 tracing-subscriber = { version = "0.3", features = ["env-filter"] }
-tree-sitter-embedded-template = "0.20"
+tree-sitter-embedded-template = "0.21"
 tree-sitter-ruby = { git = "https://github.com/tree-sitter/tree-sitter-ruby.git", rev = "bb6a42e42b048627a74a127d3e0184c1eef01de9" }