CI: ensure xz is installed for packaging jobs; check for functioning popen()

Detailed Description

Two issues which have appeared after igwn/base:conda was upgraded:

• xz is required to unpack the tarballs for the Conda/Debian/RHEL packaging jobs. The current igwn/base:conda image does not have xz installed, leading to job failures. This MR ensures that the Conda packaging jobs have xz installed; I did the same for the Debian/RHEL jobs as well for completeness. It also updates the deprecated RPM package lscsoft-packaging-tools to igwn-packaging-tools.

• The failure of lalpulsar/bin/HWInjection/test_hwinject.sh first reported in #808 (closed) is now appearing in Conda builds. Eventually identified the cause as overly pendantic error checking code; see #808 (comment 1528238). TLDR: the solution is simply to not check the value of errno unless popen() actually fails (i.e. returns NULL).

API Changes

Please tick one of the following options:

• These changes do not modify the API.
• These changes do modify the API, and are backwards compatible.
• These changes do modify the API, and are backwards incompatible.

For examples of changes that do not modify the API and/or are considered backwards (in)compatible, please see the contributing guide.

Justification for Backwards Incompatible Changes

n/a

Review Status

n/a