fix: make setup.sh executable for devcontainer postCreateCommand

[llamantino]

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• Include this change in the Release Notes. If checked, you must provide an end-user friendly description for your change below

End-user friendly description of the problem this fixes or functionality this introduces.

Fixes an issue where .devcontainer/setup.sh is not executable (+x), causing the postCreateCommand to fail with Permission denied when starting the dev container in VS Code or GitHub Codespaces.

Log from vscode:

[12906 ms] Start: Run in container: /bin/sh -c .devcontainer/setup.sh
/bin/sh: 1: .devcontainer/setup.sh: Permission denied
[13016 ms] postCreateCommand from devcontainer.json failed with exit code 126. Skipping any further user-provided commands.

Log from Codespaces:

2025-06-04 15:37:17.425Z: Error: Command failed: /bin/sh -c .devcontainer/setup.sh
2025-06-04 15:37:17.425Z: {"outcome":"error","message":"Command failed: /bin/sh -c .devcontainer/setup.sh","description":"postCreateCommand from devcontainer.json failed.","containerId":""}

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Summarize what the PR does, explaining any non-trivial design decisions.

This PR adds the executable permission (+x) to .devcontainer/setup.sh.

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Link of any specific issues this addresses: