qa/lsan.supp: suppress MallocExtension::Initialize

LeakSanitizer reports
```
==688591==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 45 byte(s) in 1 object(s) allocated from:
    #0 0x55f8dd9969dd in operator new(unsigned long) (/home/jenkins-build/build/workspace/ceph-pull-requests/build/bin/unittest_fastbmap_allocator+0x1f89dd) (BuildId: cac39eac8ef1e8774f9dd48e6e3f677fdd864776)
    #1 0x55f8dd99c730 in __gnu_cxx::new_allocator<char>::allocate(unsigned long, void const*) /usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/ext/new_allocator.h:127:27
    #2 0x55f8dd99c690 in std::allocator<char>::allocate(unsigned long) /usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/allocator.h:185:32
    #3 0x55f8dd99c690 in std::allocator_traits<std::allocator<char> >::allocate(std::allocator<char>&, unsigned long) /usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/alloc_traits.h:464:20
    #4 0x55f8dd99c393 in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_create(unsigned long&, unsigned long) /usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/basic_string.tcc:153:14
    #5 0x55f8dda96a6c in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_mutate(unsigned long, unsigned long, char const*, unsigned long) /usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/basic_string.tcc:307:21
    #6 0x55f8dda96852 in std::__cxx11::basic_string<char, std::char_traits<char>, std::allocator<char> >::_M_append(char const*, unsigned long) /usr/bin/../lib/gcc/x86_64-linux-gnu/11/../../../../include/c++/11/bits/basic_string.tcc:395:8
    #7 0x7f4a751ab6f0 in
    MallocExtension::Initialize() (/lib/x86_64-linux-gnu/libtcmalloc.so.4+0x2a6f0) (BuildId:
    eeef3d1257388a806e122398dbce3157ee568ef4)
```

this is a global object allocated by the allocator, so we can suppress this report.

Signed-off-by: Kefu Chai <tchaikov@gmail.com>

qa/lsan.supp

@@ -3,6 +3,9 @@
 # LSAN_OPTIONS="suppressions=../qa/lsan.supp"
 # export ASAN_OPTIONS="detect_odr_violation=0"
 
+# gperftools allocates a singleton of MallocExtension and never frees it
+leak:^MallocExtension::Initialize
+
 # from perfglue/heap_profiler.cc
 # gperftools allocates a singleton and never frees it
 leak:^InitModule