Update jellyseerr-install.sh: Fix pnpm version

[bvdberg01]

✍️ Description

Fix pnpm version because Jellyseerr is not compatible with pnpm 10

✅ Prerequisites

The following steps must be completed for the pull request to be considered:

• [] Self-review performed (I have reviewed my code to ensure it follows established patterns and conventions.)
• Testing performed (I have thoroughly tested my changes and verified expected functionality.)

🛠️ Type of Change

Please check the relevant options:

• Bug fix (non-breaking change that resolves an issue)
• [] New feature (non-breaking change that adds functionality)
• [] Breaking change (fix or feature that would cause existing functionality to change unexpectedly)
• [] New script (a fully functional and thoroughly tested script or set of scripts)

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📋 Additional Information (optional)

[bvdberg01]

Fixed in #2033