Add a CI check for todo! and FIXME comments (#21950)

Motivation for this is to support writing comments that will certainly
be revisited before merge.

Release Notes:

- N/A

crates/repl/src/notebook/notebook_ui.rs

@@ -515,7 +515,7 @@ impl project::ProjectItem for NotebookItem {
                     Ok(nbformat::Notebook::V4(notebook)) => notebook,
                     // 4.1 - 4.4 are converted to 4.5
                     Ok(nbformat::Notebook::Legacy(legacy_notebook)) => {
-                        // todo!(): Decide if we want to mutate the notebook by including Cell IDs
+                        // TODO: Decide if we want to mutate the notebook by including Cell IDs
                         // and any other conversions
                         let notebook = nbformat::upgrade_legacy_notebook(legacy_notebook)?;
                         notebook

crates/repl/src/outputs/markdown.rs

@@ -57,7 +57,7 @@ impl OutputContent for MarkdownView {
 
     fn buffer_content(&mut self, cx: &mut WindowContext) -> Option<Model<Buffer>> {
         let buffer = cx.new_model(|cx| {
-            // todo!(): Bring in the language registry so we can set the language to markdown
+            // TODO: Bring in the language registry so we can set the language to markdown
             let mut buffer = Buffer::local(self.raw_text.clone(), cx)
                 .with_language(language::PLAIN_TEXT.clone(), cx);
             buffer.set_capability(language::Capability::ReadOnly, cx);

crates/repl/src/session.rs

@@ -610,7 +610,7 @@ impl Session {
 
                     // Start a new kernel
                     this.update(&mut cx, |session, cx| {
-                        // todo!(): Differentiate between restart and restart+clear-outputs
+                        // TODO: Differentiate between restart and restart+clear-outputs
                         session.clear_outputs(cx);
                         session.start_kernel(cx);
                     })