BF: ignore broken derivatives

[yarikoptic]

I CPed #72 as well since otherwise couldn't install in a local venv for some reason. Most likely testing would fail probably for the same GitPython 3.x regressions as in #72 .

With this PR we will just not read derivative(s) metadata if reading them fails. Relevant issue in pybids is https://github.com/bids-standard/pybids/issues/473 which would boil down to more targetted exceptions so in the future we would be able to avoid matching a str(exc).

[jsheunis]

@yarikoptic it looks like d54ec42d98fb296908ade270fb69385dfb2fc722 is already in master, and that da72357005adf85270fe9fe062722882449377e5 would a good addition (had the same irritation with the current warning message). Anything else needed here before we can merge, apart from fixing the conflict?

[mih]

Ping @yarikoptic

[mih]

I am converting this to a draft until it is in a mergeable state again.