Replace ZLIB_ENABLE_TESTS with BUILD_TESTING

[pmqs]

Sorts out this warning

-- Fetching zlib https://github.com/zlib-ng/zlib-ng stable
-- Using CMake version 3.31.6-msvc6
-- ZLIB_HEADER_VERSION: 1.3.1
-- ZLIBNG_HEADER_VERSION: 2.3.3
CMake Deprecation Warning at third_party/zlib/CMakeLists.txt:54 (message):
  ZLIB_ENABLE_TESTS is deprecated.  Please use BUILD_TESTING instead.
-- Arch detected: 'x86_64'
...

-- The following features have been disabled:

 * ZLIB_SYMBOL_PREFIX, Publicly exported symbols DO NOT have a custom prefix
 * ZLIB_COMPAT, Compile with zlib compatible API
 * BUILD_TESTING, Build test binaries

[nmoinvaz]

Rebased.