Describe the bug

Using gh to browse a file with given line number does not work with Markdown files. The URL the user is taken to is the rendered Markdown view without line numbers on the left-hand side.

Steps to reproduce the behavior

$ gh browse README.md:3
now opening https://github.com/cli/cli/tree/trunk/README.md#L3 in browser
$ gh --version
gh version 2.0.0 (2021-08-24)
https://github.com/cli/cli/releases/tag/v2.0.0

Expected vs actual behavior

Looks like a ?plain=1 parameter was added to GitHub Web UI to specifically help navigate to Markdown lines.

So, instead of:

• https://github.com/cli/cli/tree/trunk/README.md#L3

I'd expect the user to be taken to:

• https://github.com/cli/cli/blob/trunk/README.md?plain=1#L3

note: the new URL has blob in the path because ?plain=1 does not work with tree in the path

Logs

N/A