Any test that is not tagged as :needs_network and that makes
a call to an unapproved method in the `Utils::Curl` module
will raise an error unless that method gets mocked somehow.

tests: add exceptions for tests that use curl to download local files

These are acceptable ways to use curl in local, non-network tests.
For those edge cases we allow you to bypass the check with :needs_utils_curl.

These were found with the Utils::Curl check and just turning
off the network on my computer and running the entire test suite.

This sets the HOMEBREW_NO_INSTALL_FROM_API environment variable
to prevent the selected tests from using the API. We will need
this as we transition to having the API be enabled by default
when running the tests but it's also nice as a sanity check
with the :needs_utils_curl scope in a few places.