fix(build): add default condition to platform select()

[flrgh]

Before this, non-Linux users would get this error:

(11:16:26) INFO: Current date is 2023-07-27
(11:16:26) ERROR: /path/path/path/path/external/openresty/BUILD.bazel:346:15: configurable attribute "configure_options" in @openresty//:openresty doesn't match this configuration. Would a default condition help?

Conditions checked:
 @platforms//os:linux

To see a condition's definition, run: bazel query --output=build <condition label>.

This instance of @openresty//:openresty has configuration identifier 77dabcd. To inspect its configuration, run: bazel config 77dabcd.

For more help, see https://bazel.build/docs/configurable-attributes#faq-select-choose-condition.

(11:16:26) ERROR: Analysis of target '//build:venv' failed; build aborted: 
(11:16:26) INFO: Elapsed time: 0.111s
(11:16:26) INFO: 0 processes.
(11:16:26) FAILED: Build did NOT complete successfully (0 packages loaded, 0 t\
argets configured)
source: no such file or directory: bazel-bin/build/kong-dev-venv.sh

[outsinre]

Is this required to be in EE?

[flrgh]

Is this required to be in EE?

It was already merged to EE, but it looks like the commit was squashed into a different commit: https://github.com/Kong/kong-ee/commit/ca6b40ca3818275c02ab5e9dba57af52ea26d68a

Nevertheless, it is made obsolete by this change:
https://github.com/Kong/kong-ee/pull/6189