updating node-fetch to v3

[jimmywarting]

https://github.com/angular/angularfire/blob/a26676c69790b9a236dbc08504db705f983bd8fc/site/src/shortcodes/includecode/fetch.js#L17-L31 to use latest node-fetch version you would need to use import instead of require

 async function fetchCode(githubPath) { 
   const fetch = globalThis.fetch || import('node-fetch').then(mod => mod.default);
   const githubApiUrl = convertToGitHubApiUrl(githubPath); 
   const response = await fetch(githubApiUrl); 
   return response.text(); 
 } 

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