ci: Add wrap file for libglib-testing

This is needed for building malcontent as a subproject; currently, Meson
doesn’t support recursively downloading the subprojects for nested wrap
files. (See https://github.com/mesonbuild/meson/issues/1489.) So we need
to provide `libglib-testing.wrap` in the top-level subprojects directory
in order for the `cache-subprojects.sh` script to correctly cache it in
the Docker images for CI.

Signed-off-by: Philip Withnall <withnall@endlessm.com>
3 jobs for sysprof-4-followup in 2 minutes and 48 seconds
Status Job ID Name Coverage
  Build
failed #800440
debian-stable-x86_64

00:02:15

failed #800441
fedora-x86_64

00:00:32

failed #800439
fedora-x86_64

00:00:55

 
Name Stage Failure
failed
fedora-x86_64 Build
Uploading artifacts...
WARNING: _build/config.h: no matching files
_build/meson-logs: found 2 matching files

WARNING: _build/fedora-x86_64-report.xml: no matching files
Uploading artifacts to coordinator... ok
id=800441 responseStatus=201 Created token=jk5Fbvzh
Uploading artifacts...
WARNING: _build/fedora-x86_64-report.xml: no matching files
ERROR: No files to upload
ERROR: Job failed: exit code 1
failed
debian-stable-x86_64 Build
Uploading artifacts...
_build/config.h: found 1 matching files

_build/meson-logs: found 4 matching files

_build/debian-stable-x86_64-report.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=800440 responseStatus=201 Created token=Zry96f7z
Uploading artifacts...
_build/debian-stable-x86_64-report.xml: found 1 matching files

Uploading artifacts to coordinator... ok
id=800440 responseStatus=201 Created token=Zry96f7z
ERROR: Job failed: exit code 1