fix(puppeteer): temporarily pin puppeteer version

[rwaskiewicz]

with this commit, we pin puppeteer to v21.1.1. we began to observe that our CI pipeline in Stencil core began to fail due to type errors like the following:

[ ERROR ]  TypeScript: node_modules/puppeteer/lib/types.d.ts:345:15
           Property 'asyncDispose' does not exist on type 'SymbolConstructor'.

    L344:      [Symbol_2.dispose](): void;
    L345:      [Symbol_2.asyncDispose](): Promise<void>;
    L346:  }

this occurred immediately following the puppeteer v21.2 release.

we've confirmed that 21.1.1 still works. while we works out a minimal repro case, we pin the version here to prevent folks from not being able to build

[sean-perkins]

Changes look good to me 👍 I don't have reviewer permission, but I think you can merge and by-pass branch protection here.