gh-159210: Disable virtualenv enforcement when updating certificates. (GH-159214)

Ensures that the macOS Install Certificates script can run when the user has
PIP_REQUIRE_VIRTUALENV or PIP_REQUIRE_VENV set in their shell.
(cherry picked from commit 03df941)

Co-authored-by: Russell Keith-Magee <russell@keith-magee.com>

Author: freakboy3742

Mac/BuildScript/resources/install_certificates.command

@@ -1,4 +1,8 @@
 #!/bin/sh
+# Installing into the global environment is the point; ensure that the user
+# hasn't configured pip to always require a virtual environment.
+unset PIP_REQUIRE_VENV
+unset PIP_REQUIRE_VIRTUALENV
 
 /Library/Frameworks/Python.framework/Versions/@PYVER@/bin/python@PYVER@ << "EOF"