Silence A11y warnings in build

[Fermain]

When building the LMS there are many warnings that clutter up the build log.

// packages/lms/svelte.config.js
const config = {
  // ... config
  onwarn: (warning, handler) => {
    if (warning.code.startsWith('a11y-')) {
      return;
    }
    handler(warning);
  },
}

This change will silence these warnings.