Merge branch 'ep/test-malloc-check-with-glibc-2.34'

The method to trigger malloc check used in our tests no longer work
with newer versions of glibc.

* ep/test-malloc-check-with-glibc-2.34:
  test-lib: declare local variables as local
  test-lib.sh: Use GLIBC_TUNABLES instead of MALLOC_CHECK_ on glibc >= 2.34

diff --cc t/test-lib.sh
Simple merge