Propagate GIO_PROXY_TEST_NAME to installed tests

Otherwise, the test has no way to test the proxy resolver that it claims
to test.

Part-of: <https://gitlab.gnome.org/GNOME/glib-networking/-/merge_requests/222>

Author: mcatanzaro

proxy/tests/meson.build

@@ -2,6 +2,7 @@ foreach program: proxy_test_programs
   test_conf = configuration_data()
   test_conf.set('installed_tests_dir', installed_tests_execdir)
   test_conf.set('program', program[0])
+  test_conf.set('environment', 'GIO_PROXY_TEST_NAME=' + program[1])
 
   test_name = program[0]
   if program[0] != program[1]

template.test.in

@@ -1,3 +1,3 @@
 [Test]
 Type=session
-Exec=@installed_tests_dir@/@program@
+Exec=env @environment@ @installed_tests_dir@/@program@

tls/tests/meson.build

@@ -52,6 +52,7 @@ foreach backend: backends
     test_conf = configuration_data()
     test_conf.set('installed_tests_dir', installed_tests_execdir)
     test_conf.set('program', program_name)
+    test_conf.set('environment', '')
 
     if enable_installed_tests
       configure_file(