ci: collect test coverage from qrexec-lib too

(cherry picked from commit 5961672)

.gitlab-ci.yml

@@ -1,13 +1,16 @@
 checks:tests:
   after_script:
-  - ./ci/codecov-wrapper
+  - (cd qrexec-lib; gcov *.c || :)
+  - ./ci/codecov-wrapper --gcov
   before_script:
-  - sudo dnf install -y python3-pip
+  - sudo dnf install -y python3-pip 'pkgconfig(icu-uc)'
   - export PATH="$PATH:$HOME/.local/bin"
   - pip3 install --quiet -r ci/requirements.txt
   - git config --global --add safe.directory "$PWD"
   script:
   - python3 -m coverage run -m unittest discover -v imgconverter -p test.py
+  - export CFLAGS="--coverage -DCOVERAGE" LDFLAGS=--coverage
+  - make -C qrexec-lib check NO_REBUILD_TABLE=1
   stage: checks
   tags:
   - short-living-job