when compiling the tests with -Wsign-compare, the compiler complains like:
```
/home/kefu/.local/bin/clang++ -DBOOST_ALL_DYN_LINK -DBOOST_NO_CXX98_FUNCTION_BASE -DDEBUG -DDEBUG_LSA_SANITIZER -DFMT_DEPRECATED_OSTREAM -DFMT_SHARED -DSANITIZE -DSCYLLA_BUILD_MODE=debug -DSCYLLA_ENABLE_ERROR_INJECTION -DSEASTAR_API_LEVEL=7 -DSEASTAR_BROKEN_SOURCE_LOCATION -DSEASTAR_DEBUG -DSEASTAR_DEBUG_SHARED_PTR -DSEASTAR_DEFAULT_ALLOCATOR -DSEASTAR_LOGGER_TYPE_STDOUT -DSEASTAR_SCHEDULING_GROUPS_COUNT=16 -DSEASTAR_SHUFFLE_TASK_QUEUE -DSEASTAR_TESTING_MAIN -DSEASTAR_TYPE_ERASE_MORE -DXXH_PRIVATE_API -I/home/kefu/dev/scylladb -I/home/kefu/dev/scylladb/build/cmake/gen -I/home/kefu/dev/scylladb/seastar/include -I/home/kefu/dev/scylladb/build/cmake/seastar/gen/include -isystem /home/kefu/dev/scylladb/build/cmake/rust -Wall -Werror -Wextra -Wno-error=deprecated-declarations -Wimplicit-fallthrough -Wno-c++11-narrowing -Wno-mismatched-tags -Wno-overloaded-virtual -Wno-unsupported-friend -Wno-unused-parameter -Wno-missing-field-initializers -Wno-deprecated-copy -Wno-ignored-qualifiers -march=westmere -Og -g -gz -std=gnu++20 -fvisibility=hidden -U_FORTIFY_SOURCE -DSEASTAR_SSTRING -Wno-error=unused-result "-Wno-error=#warnings" -fstack-clash-protection -fsanitize=address -fsanitize=undefined -fno-sanitize=vptr -MD -MT test/boost/CMakeFiles/tablets_test.dir/tablets_test.cc.o -MF test/boost/CMakeFiles/tablets_test.dir/tablets_test.cc.o.d -o test/boost/CMakeFiles/tablets_test.dir/tablets_test.cc.o -c /home/kefu/dev/scylladb/test/boost/tablets_test.cc
/home/kefu/dev/scylladb/test/boost/tablets_test.cc:1335:53: error: comparison of integers of different signs: 'int' and 'size_t' (aka 'unsigned long') [-Werror,-Wsign-compare]
for (int log2_tablets = 0; log2_tablets < tablet_count_bits; ++log2_tablets) {
~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~
```
in this case, it should be safe to use an signed int as the loop
variable to be compared with `tablet_count_bits`, but let's just
appease the compiler so we can enable the warning option project-wide
to prevent any potential issues caused by signed-unsigned comparision.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#15449
054beb6377