Increase challenge_prompt timeout to 60 seconds

[omus]

Change will possibly help with LibGit2 test failures which are occurring on the build bots (#27287).

[mbauman]

You're too fast! I have SSH'ed into the buildbots earlier and have been running the LibGit2 tests on the Mac buildbot with a longer timeout (I had chosen 30 seconds). That represents a hard case and I've not seen any failures yet.

Let's do this.

[mbauman]

Just as further confirmation that this is the right thing to do: I added debugging statements to look at how long the process waited on the mac buildbot. It's typically 6-8 seconds, but the occasional outlier at 11 or 12 seconds is what's been causing this to crash. With 40 or 50 challenge/response tests, it's not uncommon to hit an outlier over 10 seconds.

[omus]

@mbauman thanks for providing some empirical evidence :). The primary reason the timeout was set to a low value of 10 seconds was to avoid wasting CI time. When an unexpected prompt would appear we would need to wait for the entire timeout. If this occurs for most of the challenge prompt tests it can slow things down considerably.

[ViralBShah]

Killing the CI here, and will soon test this with the 0.7-alpha PR.