Fix code scanning alert no. 2: Prototype-polluting function

[lindluni]

Fixes https://github.com/github/safe-settings/security/code-scanning/2

To fix the prototype pollution vulnerability, we need to ensure that properties like __proto__ and constructor are not merged into the modifications, additions, or deletions objects. This can be achieved by adding checks to skip these properties during the merge process.

The best way to fix the problem without changing existing functionality is to add a condition to skip these properties in the compareDeep method. Specifically, we will add a check before processing each key to ensure it is not __proto__ or constructor.

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lib/mergeDeep.js:95

• The added condition correctly prevents prototype pollution by skipping the __proto__ and constructor properties during the merge process.

if (key === "__proto__" || key === "constructor") {

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[decyjphr]

Thanks @lindluni