Update mcp extension

[shkm]

Description

Initially I noticed that this was broken under fish. The -L argument seems to be ignored by zsh but errors in bash, and also errors in fish.

This change uses the same shell execution args for fetching env data in both cases.

Screencast

Checklist

• I read the extension guidelines
• I read the documentation about publishing
• I ran npm run build and tested this distribution build in Raycast
• I checked that files in the assets folder are used by the extension itself
• I checked that assets used by the README are placed outside of the metadata folder

[raycastbot]

Thank you for your contribution! 🎉

🔔 @EvanZhouDev @radzio you might want to have a look.

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