brave-browser: Downloading a crx file fails with CRX_REQUIRED_PROOF_MISSING on v1.40

Description

There are a couple of extensions that I use and are not in the chrome store, for unknown reasons. So, I download them and I install them manually with the procedure described below. But on v1.40, brave fails to even start the download and pops the error described in the title.

Steps to Reproduce

1. Find an extension that is packed as a crx file, e.g. the one for libredirect
2. Make sure “Ask where to save each file before downloading” (under brave://settings/downloads) is disabled.
3. Try downloading by clicking on it and notice the message on the screenshot below. Downloading it via right click > “save link as” will not produce the same behavior.

Actual result:

This error comes up and the file is either not downloaded at all or deleted instantly after download. Downloading it from firefox or with wget has no issues.

Expected result:

The file should download with no issues and I would install it manually (= go to brave://extensions > enable developer mode > drag n drop the file in the extensions window).

Reproduces how often:

Easily.

Brave version (brave://version info)

Brave	1.40.105 Chromium: 103.0.5060.53 (Official Build) (64-bit) 
Revision	a1711811edd74ff1cf2150f36ffa3b0dae40b17f-refs/branch-heads/5060@{#853}
OS	Linux

Version/Channel Information:

• Can you reproduce this issue with the current release? Yes
• Can you reproduce this issue with the beta channel? Probably
• Can you reproduce this issue with the nightly channel? Probably

Other Additional Information:

• Does the issue resolve itself when disabling Brave Shields? No
• Does the issue resolve itself when disabling Brave Rewards? No
• Is the issue reproducible on the latest version of Chrome? Yes

Miscellaneous Information:

There is another similar issue (#5524) from ~3 years ago, but that one has to do with installing while this one has to do with downloading. The fact that it also happens on chromium 103 makes me believe that some built in security policy is blocking it. It did not happen on chromium 102 or brave 1.39 (or any other previous version).