[BLD](ci): Pin minikube to 1.38.1 in tilt-setup-prebuild

[davedash]

Description

tilt-setup-prebuild uses medyagh/setup-minikube@latest with no minikube-version, so the minikube version resolves at run time. minikube 1.39.0 (picked up starting 2026-09-02) fails to start the none driver on GitHub runners: it selects the containerd runtime and setup dies with

X Exiting due to RUNTIME_ENABLE: Failed to start container runtime: Temporary Error: sudo /usr/local/bin/crictl version: exit status 1
validate CRI v1 runtime API for endpoint "unix:///run/containerd/containerd.sock": rpc error: code = Unimplemented desc = unknown service runtime.v1.RuntimeService

This broke every hosted-chroma tilt CI job today (this repo's own tilt jobs consume the same action). The last job to pass used 1.38.1 (2026-09-01); the first to fail used 1.39.0 — reruns reproduce it deterministically.

Change

Pin minikube-version: 1.38.1 (last known good). We can unpin or bump once minikube's none-driver regression is fixed upstream.

Validation

• Failing hosted runs: js, JS (E2E) — both die in minikube setup before any test runs.
• Passing 1.38.1 run for contrast: JS (E2E) on hosted #8324.
• This PR's own CI exercises the pinned action.

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