fix(appImage): Bundle libpangocairo which was incompatible on Arch

No systematic fix to the constant flakiness of AppImage. Although we could
upload the artifact in a job and download in on another job's platform,
minimal docker images aren't analogous to user desktop systems. AppImage
and linuxdeployqt specifically make assumptions about what libs should
exist, so our testing should be more real-world.

Will continue manually testing in full desktop VMs before release and
relying on user reports.

Fix #6454

appimage/build.sh

@@ -97,6 +97,7 @@ libs=(
 /usr/lib/x86_64-linux-gnu/libgio-2.0.so.0
 /usr/lib/x86_64-linux-gnu/libpango-1.0.so.0
 /usr/lib/x86_64-linux-gnu/libpangoft2-1.0.so.0
+/usr/lib/x86_64-linux-gnu/libpangocairo-1.0.so.0
 )
 
 for lib in "${libs[@]}"; do