fix: always write with utf8 encoding

[dolfim-ibm]

Automatic fixes done with

ruff check --preview --select PLW1514 --fix --unsafe-fixes

credits to https://github.com/tiran for finding it.

[mergify]

Merge Protections

Your pull request matches the following merge protections and will not be merged until they are valid.

🟢 Enforce conventional commit

Wonderful, this rule succeeded.

Make sure that we follow https://www.conventionalcommits.org/en/v1.0.0/

• title ~= ^(fix|feat|docs|style|refactor|perf|test|build|ci|chore|revert)(?:\(.+\))?(!)?:

🟢 Require two reviewer for test updates

Wonderful, this rule succeeded.

When test data is updated, we require two reviewers

• #approved-reviews-by >= 2

[PeterStaar-IBM]

good catch!