fix: remove schema validation from feature release flow (#6945)

# Description

The GitHub Action workflow currently fails (see
https://github.com/radius-project/radius/actions/runs/7183715348) due to
the usage of preview features in the devcontainer feature schema (for
details see PR #6930)
This PR contains a fix to allow the release of the devcontainer feature
even when suing preview features in the schema.

## Type of change

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- This pull request is a minor refactor, code cleanup, test improvement,
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Fixes: n/a

## Auto-generated summary

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### Summary
🛠️🚀🐳

<!--
1. 🛠️ - This emoji represents a tool or fixing something, and can be
used to indicate that the schema validation was disabled to avoid errors
and enable the workflow to run properly.
2. 🚀 - This emoji represents launching or deploying something, and can
be used to indicate that the workflow uses a preview feature (the
`pull_request_target` event) that allows it to run on pull requests from
forks and merge them to the main branch when ready.
3. 🐳 - This emoji represents a whale or Docker, and can be used to
indicate that the workflow builds and tests the devcontainer feature
branch, which is related to using Docker containers for development
environments.
-->
Disable schema validation for devcontainer feature release workflow.
This fixes a compatibility issue with a preview GitHub Actions feature
and allows the workflow to run on pull requests from forks.

> _`pull_request_target`_
> _Preview feature, no schema_
> _Workflow runs in fall_

### Walkthrough
* Disable schema validation for GitHub Actions workflow to use preview
feature `pull_request_target`
([link](https://github.com/radius-project/radius/pull/6945/files?diff=unified&w=0#diff-786e5036d5206693ef00172e6655e7b814833b8a1117ffed490dd9178f7e2d77R29-R30))

Signed-off-by: Christian Lechner <[email protected]>

Author: lechnerc77

.github/workflows/devcontainer-feature-release.yaml

@@ -26,6 +26,8 @@ jobs:
           publish-features: "true"
           base-path-to-features: "./deploy/devcontainer-feature/src"
           generate-docs: "false"
+          # disable validation due to used preview feature
+          disable-schema-validation: "true"
 
         env:
           GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}