Add a unit test for function AVERAGE with non-numeric named expressions

[sequba]

Context

TBP

How did you test your changes?

TBP

Types of changes

• Breaking change (a fix or a feature because of which an existing functionality doesn't work as expected anymore)
• New feature or improvement (a non-breaking change that adds functionality)
• Bug fix (a non-breaking change that fixes an issue)
• Additional language file, or a change to an existing language file (translations)
• Change to the documentation

Related issues:

Fixes #1389

Checklist:

• I have reviewed the guidelines about Contributing to HyperFormula and I confirm that my code follows the code style of this project.
• I have signed the Contributor License Agreement.
• My change is compliant with the OpenDocument standard.
• My change is compatible with Microsoft Excel.
• My change is compatible with Google Sheets.
• I described my changes in the CHANGELOG.md file.
• My changes require a documentation update.
• My changes require a migration guide.

[github-actions]

Performance comparison of head (242815d) vs base (e32e132)

 testName | base | head | change ------------------------------------------------------------------------ Sheet A | 525.73 | 531.41 | +1.08% Sheet B | 169.94 | 172.37 | +1.43% Sheet T | 149.4 | 150.82 | +0.95% Column ranges | 547.26 | 549.92 | +0.49% Sheet A: change value, add/remove row/column | 15.12 | 14.18 | -6.22% Sheet B: change value, add/remove row/column | 131.3 | 135 | +2.82% Column ranges - add column | 155.5 | 155.87 | +0.24% Column ranges - without batch | 455.33 | 465.32 | +2.19% Column ranges - batch | 117.39 | 123.49 | +5.20%