Add TestPanic feature flag (#34963)

Now the `dev: panic` action can be run on all release channels if the
user has the feature flag enabled.

Release Notes:

- N/A

crates/zed/Cargo.toml

@@ -56,6 +56,7 @@ env_logger.workspace = true
 extension.workspace = true
 extension_host.workspace = true
 extensions_ui.workspace = true
+feature_flags.workspace = true
 feedback.workspace = true
 file_finder.workspace = true
 fs.workspace = true