Use fixed commit hash, ref #13089

[rzhao271]

Ref #13089

Use a fixed commit hash to control when we want to update the ref to the upstream script.
Otherwise, we might get hit by that script updating and breaking our CI.

CC @Tyriar

TODO:

• Custom Insiders build passes
• Deb package is sane
• PR is reviewed

[rzhao271]

Did a small search.
https://github.com/electron/electron/tree/6165f6afc9af6f9ab4e32f4a7a8b0818f11e766a is the commit for 18.3.5.
The DEPS file shows the Chromium version is 100.0.4896.160.
It turns out we can use that version number directly.

[rzhao271]

I manually verified that the dependencies list stayed the same, forgetting that the CI build checks that already 🤦‍♂️