[BLD]: invalidate the layer cache for git clone hnswlib when there's …

…a new commit to the repo (#3258)

## Description of changes

Rust image builds are currently failing because an older, cached version
of hnswlib is being used.

## Test plan
*How are these changes tested?*

- [x] Tests pass locally with `pytest` for python, `yarn test` for js,
`cargo test` for rust

## Documentation Changes
*Are all docstrings for user-facing APIs updated if required? Do we need
to make documentation changes in the [docs
repository](https://github.com/chroma-core/docs)?*

n/a

rust/worker/Dockerfile

@@ -3,6 +3,9 @@ FROM rust:1.81.0 AS builder
 ARG RELEASE_MODE=
 
 WORKDIR /
+
+# ADD with an external URL is always run, so this will trigger a cache invalidation (and thus run the below git clone) if the latest commit changes
+ADD "https://api.github.com/repos/chroma-core/hnswlib/commits?per_page=1" hnswlib_commits.json
 RUN git clone https://github.com/chroma-core/hnswlib.git
 
 WORKDIR /chroma/