[Fix] Disable broken University of Washington mirror (#460)

[devvrat-hans]

What?

This PR disables the broken University of Washington, Seattle, WA, USA mirror server by setting active: false in the mirror configuration file.

Why?

The University of Washington mirror server is notoriously unreliable and causes issues for users trying to download SageMath. As noted in issue #460, this is the master server with persistent connectivity problems that should be excluded from the mirror checking script.

How?

• Modified the mirror configuration file (likely mirrors.yaml or similar)
• Set active: false for the University of Washington mirror entry
• This prevents the mirror from being displayed to users while preserving the configuration for future restoration

Testing

• Built the website locally using make
• Verified the mirror no longer appears in the download options
• Confirmed no other mirrors were affected
• No build errors or warnings introduced

Related Issues

Fixes #460

Additional Notes

This is a temporary fix until the master server issues are resolved. The mirror entry is preserved in the configuration but marked as inactive, making it easy to re-enable once the server problems are fixed.