ci: use timeout-multiplier=2 for running the tests

It looks like the coverage generation makes the tests a bit slower and
some are now hitting timeouts. Flaky tests are always more annoying than
slow ones, and we don't know how much resources we get under CI,
so increase the timeout.

https://bugzilla.gnome.org/show_bug.cgi?id=795636

.gitlab-ci.yml

@@ -17,7 +17,7 @@ fedora-meson-x86_64:
     - meson --prefix /usr --libdir /usr/lib64 --buildtype debug --werror -Dsystemtap=true -Ddtrace=true _build .
     - cd _build
     - ninja
-    - meson test
+    - meson test --timeout-multiplier 2
     - cd ..
     - mkdir -p _coverage
     - lcov --rc lcov_branch_coverage=1 --directory . --capture --no-external --output-file "_coverage/${CI_JOB_NAME}.lcov"