Adding upstream version 9.0.6.

Signed-off-by: Daniel Baumann <daniel@debian.org>

CONTRIBUTING.md

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+# Contributing to [SQLGlot](https://github.com/tobymao/sqlglot/blob/main/README.md)
+
+SQLGLot is open source software. We value feedback and we want to make contributing to this project as
+easy and transparent as possible, whether it's:
+
+- Reporting a bug
+- Discussing the current state of the code
+- Submitting a fix
+- Proposing new features
+
+## We develop with Github
+We use github to host code, to track issues and feature requests, as well as accept pull requests.
+
+## Submitting code changes
+Pull requests are the best way to propose changes to the codebase. We actively welcome your pull requests:
+
+1. Fork the repo and create your branch from `main`.
+2. If you've added code that should be tested, add tests.
+3. If you've changed APIs, update the documentation.
+4. Ensure the test suite & linter [checks](https://github.com/tobymao/sqlglot/blob/main/README.md#run-tests-and-lint) pass.
+5. Issue that pull request and wait for it to be reviewed by a maintainer or contributor!
+
+## Report bugs using Github's [issues](https://github.com/tobymao/sqlglot/issues)
+We use GitHub issues to track public bugs. Report a bug by [opening a new issue]().
+
+**Great Bug Reports** tend to have:
+
+- A quick summary and/or background
+- Steps to reproduce
+  - Be specific!
+  - Give sample code if you can
+- What you expected would happen
+- What actually happens
+- Notes (possibly including why you think this might be happening, or stuff you tried that didn't work)
+
+## Start a discussion using Github's [discussions](https://github.com/tobymao/sqlglot/discussions)
+[We use GitHub discussions](https://github.com/tobymao/sqlglot/discussions/190) to discuss about the current state
+of the code. If you want to propose a new feature, this is the right place to do it! Just start a discussion, and
+let us know why you think this feature would be a good addition to SQLGlot (by possibly including some usage examples).
+
+## [License](https://github.com/tobymao/sqlglot/blob/main/LICENSE)
+By contributing, you agree that your contributions will be licensed under its MIT License.
+
+## References
+This document was adapted from [briandk's template](https://gist.github.com/briandk/3d2e8b3ec8daf5a27a62).