Fix for unicode in test Any file headers

[JDThomsen]

This pull request makes small improvements to file handling in anypytools/pytest_plugin.py by explicitly specifying UTF-8 encoding when reading and writing files. This helps ensure consistent behavior across different environments and avoids encoding-related issues.

• File reading improvements:

  • Updated the _read_header function to open files with encoding='utf8' for consistent text decoding.

• File writing improvements:

  • Updated the _write_macro_file function to open files with encoding='utf8' for consistent text encoding.

[melund]

I just fixed one extra instance where utf8 specification was missing. Also added an changelog entry and bumped the version for a release.