CI: Add zlib into the Conda env file

[certik]

No description provided.

[certik]

This is trying to fix the failure in master at the CI for macOS and Windows: https://github.com/lcompilers/lpython/runs/7817883741?check_suite_focus=true:

CMake Error at /usr/local/Cellar/cmake/3.24.0/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:230 (message):
  Could NOT find ZLIB (missing: ZLIB_LIBRARY) (found version "1.2.11")
Call Stack (most recent call first):
  /usr/local/Cellar/cmake/3.24.0/share/cmake/Modules/FindPackageHandleStandardArgs.cmake:594 (_FPHSA_FAILURE_MESSAGE)
  /usr/local/Cellar/cmake/3.24.0/share/cmake/Modules/FindZLIB.cmake:150 (FIND_PACKAGE_HANDLE_STANDARD_ARGS)
  cmake/FindStaticZLIB.cmake:7 (find_package)
  CMakeLists.txt:85 (find_package)

[czgdp1807]

Seems to work, so approving.