Fix typos in modern_iau sky culture

[martignoni]

Description

Fix typos in modern_iau sky culture

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• This change requires a documentation update
• Housekeeping

How Has This Been Tested?

Test Configuration:

• Operating system: <Name, version number>
• Graphics Card: <Manufacturer (likely Intel, NVidia, AMD?), Model (HD, Geforce, Radeon..., with model number), driver version?>

Checklist:

• My code follows the code style of this project.
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (header file)
• I have updated the respective chapter in the Stellarium User Guide
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[github-actions]

Great PR! Please pay attention to the following items before merging:

Files matching skycultures/**:

• Did you remember to update po/stellarium-skycultures/POFILES.in file respectively to changes in sky cultures?
• Did you remember to update skycultures/CMakeLists.txt and skycultures/YOUR-SKYCULTURE-FOLDER/CMakeLists.txt files respectively to changes in sky cultures?
• Did you remember to update util/skycultures/po4a.config file respectively to changes in sky cultures?
• Did you remember to define classification parameter in sky cultures (see info.ini file)?
• Did you remember to define license parameter in sky cultures (see info.ini file)?
• Did you remember to define region parameter in sky culture (see info.ini file)?

This is an automatically generated QA checklist based on modified files.

[alex-w]

Thanks!