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

Cargo.lock

@@ -3790,6 +3790,7 @@ dependencies = [
  "node_runtime",
  "parking_lot",
  "project",
+ "release_channel",
  "schemars",
  "semantic_version",
  "serde",
@@ -3844,6 +3845,7 @@ dependencies = [
  "language",
  "picker",
  "project",
+ "release_channel",
  "semantic_version",
  "serde",
  "settings",