Enable test suite by default

Rather than making tests opt in, make them opt out.  Distros should
be running tests in their infrastructure as well during build time.

.gitlab-ci.yml

@@ -46,7 +46,6 @@ build_stable:
         --warnlevel 2
         -Dgtk_doc=true
         -Dpylint=true
-        -Dtests=true
         -Db_coverage=true
         _build
     - env TMPDIR=$(pwd)/tmpdir meson test -C _build --print-errorlogs

meson_options.txt

@@ -13,4 +13,4 @@ option('pylint',
 option('tests',
        description: 'Whether to run tests',
        type: 'boolean',
-       value: false)
+       value: true)