tests: Give mutter-test-runner the RUNPATH to find Clutter

Until recently, mutter-test-runner called into libraries that
indirectly depend on (mutter's fork of) Clutter, but did not actually
call into Clutter itself. Commit 1bf70334 "tests/runner: Make test
runner use the headless backend" gave it a direct call into Clutter,
which means the runtime linker will fail unless the executable's
RUNPATH is sufficient to find Clutter.

For future-proofing, do the same for the other test executables.

Resolves: https://gitlab.gnome.org/GNOME/mutter/-/issues/2389
Signed-off-by: Simon McVittie <smcv@debian.org>
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2581>

src/tests/meson.build

@@ -128,6 +128,7 @@ test_client = executable('mutter-test-client',
   ],
   install: have_installed_tests,
   install_dir: mutter_installed_tests_libexecdir,
+  install_rpath: pkglibdir,
 )
 
 test_runner = executable('mutter-test-runner',
@@ -142,6 +143,7 @@ test_runner = executable('mutter-test-runner',
   dependencies: libmutter_test_dep,
   install: have_installed_tests,
   install_dir: mutter_installed_tests_libexecdir,
+  install_rpath: pkglibdir,
 )
 
 meta_dbus_runner = find_program('meta-dbus-runner.py')
@@ -240,6 +242,7 @@ if have_native_tests
     ],
     install: have_installed_tests,
     install_dir: mutter_installed_tests_libexecdir,
+    install_rpath: pkglibdir,
   )
 
   # Native backend tests
@@ -374,6 +377,7 @@ if have_native_tests
       dependencies: libmutter_test_dep,
       install: have_installed_tests,
       install_dir: mutter_installed_tests_libexecdir,
+      install_rpath: pkglibdir,
     )
 
     test(test_case['name'], test_executable,
@@ -447,6 +451,7 @@ if have_kvm_tests or have_tty_tests
       dependencies: libmutter_test_dep,
       install: have_installed_tests,
       install_dir: mutter_installed_tests_libexecdir,
+      install_rpath: pkglibdir,
     )
 
     foreach variant: variants