Add python dependency to google-cloud-sdk (#96091)

* Previous PR removes python dep instead of update

The previous PR I wrote for this was intended to update to use the
current version of python considered default by homebrew. While much of
the PR was correct I inadvertently removed the dependency on python
instead of allowing the default.

* Use default `python` instead of `python@3.9`

Co-authored-by: Markus Reiter <me@reitermark.us>

* testing env spec

* force use of brew python for install

* Update google-cloud-sdk.rb

Co-authored-by: Evan Pitstick <epitstick@paloaltonetworks.com>
Co-authored-by: Markus Reiter <me@reitermark.us>

Casks/google-cloud-sdk.rb

@@ -7,6 +7,8 @@ cask "google-cloud-sdk" do
   desc "Set of tools to manage resources and applications hosted on Google Cloud"
   homepage "https://cloud.google.com/sdk/"
 
+  depends_on formula: "python"
+
   stage_only true
 
   postflight do
@@ -14,7 +16,8 @@ cask "google-cloud-sdk" do
                    args: [
                      "--usage-reporting", "false", "--bash-completion", "false", "--path-update", "false",
                      "--rc-path", "false", "--quiet"
-                   ]
+                   ],
+                   env:  { "CLOUDSDK_PYTHON" => Formula["python"].opt_bin/"python3" }
   end
 
   # Not actually necessary, since it would be deleted anyway.