chore(ci): skip non-linux OCI package creation (#12036)

The shared pipeline is introducing support for windows OCI packages.
This PR ensure dd-trace-py doesn't generate nonsensical packages.
Windows support can be added later.

This was tested by using the WIP branch of one-pipeline

## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [x] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

---------

Co-authored-by: Brett Langdon <[email protected]>

.gitlab/prepare-oci-package.sh

@@ -1,6 +1,11 @@
 #!/bin/bash
 set -eo pipefail
 
+if [ "$OS" != "linux" ]; then
+  echo "Only linux packages are supported. Exiting"
+  exit 0
+fi
+
 if [ -n "$CI_COMMIT_TAG" ] && [ -z "$PYTHON_PACKAGE_VERSION" ]; then
   PYTHON_PACKAGE_VERSION=${CI_COMMIT_TAG##v}
 fi