Restrict v0.0.7 of the zed_extension_api to dev builds, for now (#12170)

This PR restricts usage of v0.0.7 of the `zed_extension_api` to dev
builds, for now.

As we're still making changes to it, we don't want to ship a version of
Zed to Preview/Stable that claims to support a yet-unreleased version of
the extension API.

Release Notes:

- N/A

crates/extension/src/extension_store_test.rs

@@ -714,6 +714,7 @@ fn init_test(cx: &mut TestAppContext) {
     cx.update(|cx| {
         let store = SettingsStore::test(cx);
         cx.set_global(store);
+        release_channel::init("0.0.0", cx);
         theme::init(theme::LoadThemes::JustBase, cx);
         Project::init_settings(cx);
         ExtensionSettings::register(cx);