Fix broken link to LCOV (#1356)

Author: tomasr8

testing/coverage.rst

@@ -306,5 +306,5 @@ about 20 to 30 minutes on a modern computer.
 
 .. _issue tracker: https://github.com/python/cpython/issues
 .. _gcov: https://gcc.gnu.org/onlinedocs/gcc/Gcov.html
-.. _lcov: https://ltp.sourceforge.net/coverage/lcov.php
+.. _lcov: https://github.com/linux-test-project/lcov
 .. _coverage.py: https://coverage.readthedocs.io/en/latest/