Add missing xmllint dependency for capgen tests

[mwaxmonsky]

Add missing xmllint dependency for capgen tests

Adds the libxml2-utils dependency to allow full capgen tests to run without printing an error message about a missing dependency

User interface changes?: No

Fixes: closes #601 (by adding missing dependency)

Testing:
test removed: None
unit tests: CI run
system tests: N/A
manual testing: N/A

[climbfuji]

This is still a draft, but I approve since the error message is no longer in the CI output. Thanks for fixing this.

[mwaxmonsky]

This is still a draft, but I approve since the error message is no longer in the CI output. Thanks for fixing this.

No problem! I was going to leave it in draft until we decided on how we wanted to handle the internal check for xmllint (opt-in vs. opt-out) but if it makes sense to hold that off for another PR/discussion, I'm happy to get this in sooner rather than later.

[mwaxmonsky]

This is still a draft, but I approve since the error message is no longer in the CI output. Thanks for fixing this.

No problem! I was going to leave it in draft until we decided on how we wanted to handle the internal check for xmllint (opt-in vs. opt-out) but if it makes sense to hold that off for another PR/discussion, I'm happy to get this in sooner rather than later.

Based on our discussion yesterday, I will patch the missing dependency here only and open another issue to implement the opt-out flag implementation separately.