`zlib` download fails

[tbirdso]

[7/40] Performing download step (git clone) for 'zlib'
FAILED: zlib-prefix/src/zlib-stamp/zlib-download 
cd /home/runner/work/bld && /home/runner/work/_temp/685782585/cmake-3.18.3-Linux-x86_64/bin/cmake -P /home/runner/work/bld/zlib-prefix/tmp/zlib-gitclone.cmake && /home/runner/work/_temp/685782585/cmake-3.18.3-Linux-x86_64/bin/cmake -E touch /home/runner/work/bld/zlib-prefix/src/zlib-stamp/zlib-download
Cloning into 'zlib'...
fatal: remote error: 
  The unauthenticated git protocol on port 9418 is no longer supported.
Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/ for more information.
Cloning into 'zlib'...
fatal: remote error: 
  The unauthenticated git protocol on port 9418 is no longer supported.
Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/ for more information.
Cloning into 'zlib'...
fatal: remote error: 
  The unauthenticated git protocol on port 9418 is no longer supported.
Please see https://github.blog/2021-09-01-improving-git-protocol-security-github/ for more information.
-- Had to git clone more than once:
          3 times.
CMake Error at zlib-prefix/tmp/zlib-gitclone.cmake:31 (message):
  Failed to clone repository: 'git://github.com/commontk/zlib.git'

Per discussion in #327 this may be resolved by forcing https in place of git.