[#3] Set 'RUSTFLAGS' as global env variable on cirrus ci

[elBoberido]

Notes for Reviewer

On Cirrus-CI the test tasks are build with different flags than the build tasks. This results in rebuilding everything for the tests and increases the CI time quite a lot for the aarch64 release builds.

This PR sets the RUSTFLAGS in a global environment variable, similar to the github actions.

Pre-Review Checklist for the PR Author

1. [x] Add sensible notes for the reviewer
2. [x] PR title is short, expressive and meaningful
3. [x] Relevant issues are linked in the References section
4. [x] Every source code file has a copyright header with SPDX-License-Identifier: Apache-2.0 OR MIT
5. [x] Branch follows the naming format (iox2-123-introduce-posix-ipc-example)
6. [x] Commits messages are according to this guideline
   • [x] Commit messages have the issue ID ([#123] Add posix ipc example)
   • [x] Commit author matches Eclipse Contributor Agreement (and ECA is signed)
7. [x] Tests follow the best practice for testing
8. [x] Changelog updated in the unreleased section including API breaking changes
9. [x] Assign PR to reviewer
10. [x] All checks have passed (except task-list-completed)

Checklist for the PR Reviewer

• [x] Commits are properly organized and messages are according to the guideline
• [x] Unit tests have been written for new behavior
• [x] Public API is documented
• [x] PR title describes the changes

Post-review Checklist for the PR Author

1. [x] All open points are addressed and tracked via issues

References

Relates to #3

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 80.02%. Comparing base (2626216) to head (b5efff4).

Additional details and impacted files

[](https://app.codecov.io/gh/eclipse-iceoryx/iceoryx2/pull/228?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=eclipse-iceoryx) ```diff @@ Coverage Diff @@ ## main #228 +/- ## ========================================== - Coverage 80.02% 80.02% -0.01% ========================================== Files 183 183 Lines 20426 20426 ========================================== - Hits 16346 16345 -1 - Misses 4080 4081 +1 ``` [see 4 files with indirect coverage changes](https://app.codecov.io/gh/eclipse-iceoryx/iceoryx2/pull/228/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=eclipse-iceoryx)