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/appinfo-test-static.desktop

@@ -0,0 +1,19 @@
+[Desktop Entry]
+Type=Application
+GenericName=generic-appinfo-test
+Name=appinfo-test
+Name[de]=appinfo-test-de
+X-GNOME-FullName=example
+X-GNOME-FullName[de]=Beispiel
+Comment=GAppInfo example
+Comment[de]=GAppInfo Beispiel
+Exec=true --option %U %i --name %c --filename %k %m %%
+Icon=testicon.svg
+Terminal=true
+StartupNotify=true
+StartupWMClass=appinfo-class
+MimeType=image/png;image/jpeg;
+Keywords=keyword1;test keyword;
+Categories=GNOME;GTK;
+X-JunkFood=Burger
+X-JunkFood[de]=Bratwurst