gh-actions: remove reporting release tests to Matrix

[miri64]

Contribution description

Reporting the release tests to Matrix never really worked and currently it makes the release tests look like failing. So lets just remove this action.

This effectively reverts commits 9810070 and 764f7f0.

Testing procedure

Release tests should still work... we can start a run, but since this just reverts the to commits that added this which are the two last changes in the log to tha workflow file, I am pretty confident that this does not break anything:

$ git log upstream/master -- .github/workflows/release-test.yml
commit 98100704ab74a7163bb2a32c4d1d4c25a6ad588a
Author: Martine Lenders <m.lenders@fu-berlin.de>
Date:   Sat Jan 14 09:49:52 2023 +0100

    release-tests: fix PASSED chat message

commit 764f7f0bf4cff93676f830e5bad441e534a20b1e
Author: Martine Lenders <m.lenders@fu-berlin.de>
Date:   Fri Jan 6 14:24:17 2023 +0100

    gh-actions: report release-tests result to Matrix

commit 37be7b9420c5735968139e6261e1e7b1b990629c
Author: Martine Lenders <m.lenders@fu-berlin.de>
Date:   Thu Oct 13 18:05:07 2022 +0200

    Revert "release-tests: add capability to run on PR comment"

[...]

Issues/PRs references

Reverts #19102 and #19145.

[riot-ci]

Murdock results

✔️ PASSED

fec3c24 gh-actions: remove reporting release tests to Matrix

Success	Failures	Total	Runtime
1	0	1	59s

Artifacts

• Documentation preview

[miri64]

bors merge

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• Murdock
• static-tests
• tools-build-success