Remove Cython future warning

[oscargus]

References to other Issues or PRs

Brief description of what is fixed or changed

Fixes the following warning in optional dependency-tests by setting language_level to 3 if it is not explicitly set elsewhere:

/opt/hostedtoolcache/Python/3.9.9/x64/lib/python3.9/site-packages/Cython/Compiler/Main.py:369: FutureWarning: Cython directive 'language_level' not set, using 2 for now (Py2). This will change in a later release! File: /tmp/tmp4y6wzijg/_sigmoid.pyx

Other comments

Release Notes

• utilities
  • language_level is automatically set to 3 when compiling with cython using utilities._compilation, but can be overridden by providing another language_level.

[sympy-bot]

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Here is what the release notes will look like:

• utilities
  • language_level is automatically set to 3 when compiling with cython using utilities._compilation, but can be overridden by providing another language_level. (#22742 by @oscargus and @sympy)

This will be added to https://github.com/sympy/sympy/wiki/Release-Notes-for-1.10.

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#### References to other Issues or PRs
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#### Brief description of what is fixed or changed

Fixes the following warning in optional dependency-tests by setting language_level to 3 if it is not explicitly set elsewhere:
```
/opt/hostedtoolcache/Python/3.9.9/x64/lib/python3.9/site-packages/Cython/Compiler/Main.py:369: FutureWarning: Cython directive 'language_level' not set, using 2 for now (Py2). This will change in a later release! File: /tmp/tmp4y6wzijg/_sigmoid.pyx
```

#### Other comments


#### Release Notes

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  * Added a new solver for logarithmic equations.

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  * Fixed a bug with log of integers.

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<!-- BEGIN RELEASE NOTES -->
* utilities
    * `language_level` is automatically set to 3 when compiling with cython using `utilities._compilation`, but can be overridden by providing another language_level.
<!-- END RELEASE NOTES -->

Update

The release notes on the wiki have been updated.