Revert "chore(deps): update dependency symbol-observable to v3 (#7299)"

[benjamn]

This reverts commit 2809d6d, hopefully fixing issue #7337. The problem is not the @types/node version, as conjectured in #7335, but the incompatibility between the version of @types/node used by Angular and the major update of symbol-observable, which is a non-dev dependency of @apollo/client:

ERROR in node_modules/@apollo/client/node_modules/symbol-observable/index.d.ts:6:14 - error TS2717: Subsequent property declarations must have the same type.  Property 'observable' must be of type 'symbol', but here has type 'unique symbol'.

    6     readonly observable: unique symbol;
                   ~~~~~~~~~~

      node_modules/@types/node/globals.d.ts:146:14
        146     readonly observable: symbol;
                         ~~~~~~~~~~
        'observable' was also declared here.

[benjamn]

Thanks to @matt-goldman's reproduction steps in #7337, I can confirm that this PR fixes the problem.