Fix FORCE_INSTALL when using simple install commands

[db39]

Resolves #1864

This change updates get-install.sh to preserve the FORCE_INSTALL environment variable when running sudo ./install.

This allows users to set FORCE_INSTALL before running the simple install commands.

To test live on a device, install Raspberry Pi OS Bullseye 32-bit and run:

export FORCE_INSTALL=1

And then:

curl \
  --silent \
  --show-error \
  https://raw.githubusercontent.com/tiny-pilot/tinypilot/refs/heads/1864-force_install-doesnt-work-as-expected/get-tinypilot.sh | \
    bash - && \
  sudo reboot

[db39]

Automated comment from CodeApprove ➜

⏳ @cghague please review this Pull Request

[cghague]

Automated comment from CodeApprove ➜

✔️ Approved

LGTM

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👀 @db39 it's your turn please take a look