Fix watch for block+closure split (#7374)

The block+closure split broke `watch` for some use cases. Fixed.

We should eventually add some tests for `watch` but it's a little tricky
since it's an interactive command.

Closes #7362.

crates/nu-command/src/filesystem/watch.rs

@@ -35,7 +35,9 @@ impl Command for Watch {
  fn signature(&self) -> nu_protocol::Signature {
  Signature::build("watch")
  .required("path", SyntaxShape::Filepath, "the path to watch. Can be a file or directory")
- .required("block", SyntaxShape::Block, "A Nu block of code to run whenever a file changes. The block will be passed `operation`, `path`, and `new_path` (for renames only) arguments in that order")
+ .required("closure",
+ SyntaxShape::Closure(Some(vec![SyntaxShape::String, SyntaxShape::String, SyntaxShape::String])),
+ "Some Nu code to run whenever a file changes. The closure will be passed `operation`, `path`, and `new_path` (for renames only) arguments in that order")
  .named(
  "debounce-ms",
  SyntaxShape::Int,