tests: fix memory leak in proxy-test
When running tests with ASan, proxy-test fails at the proxy_tag test:
==27843==ERROR: LeakSanitizer: detected memory leaks
Direct leak of 32 byte(s) in 1 object(s) allocated from:
#0 0x7f65a732dada in __interceptor_malloc /build/gcc/src/gcc/libsanitizer/asan/asan_malloc_linux.cc:144
#1 0x7f65a71cb3ea in wl_display_add_protocol_logger src/wayland-server.c:1813
#2 0x557c640c0980 in proxy_tag tests/proxy-test.c:104
#3 0x557c640c1159 in run_test tests/test-runner.c:153
#4 0x557c640c1e2e in main tests/test-runner.c:337
#5 0x7f65a6ea0ee2 in __libc_start_main (/usr/lib/libc.so.6+0x26ee2)
SUMMARY: AddressSanitizer: 32 byte(s) leaked in 1 allocation(s).
Destroying the logger fixes the leak.
Signed-off-by: Simon Ser contact@emersion.fr Fixes: 493ab79b ("proxy: Add API to tag proxy objects")