check that patches are not broken

[mockersf]

Objective

• Fixes Check example showcase patches in CI #12441
• check that patches are still working

Solution

• Apply all patches then build Bevy

[rparrett]

I was slightly worried about contributor experience here. A failure currently looks like:

Where

• CI doesn't tell you which patch failed, so that needs to be cross-referenced
• CI stops after the first failure

But with this running on merge_group, I guess it's mostly maintainers having to deal with / at least explain this to contributors?

Still, would something like this be helpful? (or maybe just a set -x)

CODE=0
for patch in tools/example-showcase/*.patch; do
  git apply --ignore-whitespace $patch || { echo "::error::$patch failed to apply."; CODE=1; }
done
exit $CODE

(output using that code here: https://github.com/rparrett/bevy/actions/runs/8286681390/job/22677245376#step:7:14)

[mockersf]

But with this running on merge_group, I guess it's mostly maintainers having to deal with / at least explain this to contributors?

What worries me most is that git is not an easy tool to master, and I'm not sure how to write an error message that would teach anyone how to create a patch

[BD103]

I know I'm a bit late, but does this need to install cargo-udeps if we're just calling cargo build? Was this leftover from a copy-paste?