tests: Use static appinfo .desktop file when not launching

The appinfo-test.desktop file is set up with an Exec= path which points
to the compiled and installed appinfo-test utility. When running the
tests uninstalled, however, this might not be present, which causes
loading appinfo-test.desktop to fail.

Split appinfo-test.desktop in two: keep the existing
appinfo-test.desktop for tests which need to launch appinfo-test, and
add a new appinfo-test-static.desktop for tests which don’t launch
anything (and, for example, just inspect GAppInfo properties).
appinfo-test-static.desktop uses an Exec= line which should always be
present (`true`) so it should never fail to load.

Allow the tests using appinfo-test-static.desktop to be run uninstalled
or installed. Allow the tests using appinfo-test.desktop to be skipped
if loading appinfo-test.desktop fails, which is an indicator that the
test is running uninstalled.

Signed-off-by: Philip Withnall <withnall@endlessm.com>

gio/tests/meson.build

@@ -424,6 +424,7 @@ if installed_tests_enabled
     'contexts.c',
     'g-icon.c',
     'appinfo-test-actions.desktop',
+    'appinfo-test-static.desktop',
     'file.c',
     'org.gtk.test.dbusappinfo.desktop',
     install_dir : installed_tests_execdir,