Update schema with '--diff' creates new schema if new version is set

[ErichSuter]

Command: ./tools/update-schemas
The command handles a set of options.

When specifying --diff, it is expected that no file should be created or modified.
But if a new version is specified, e.g. changing 0.10.0 to 0.11.0 in
https://github.com/equinor/fmu-dataio/blob/ce7ef54f6344de5a3ac503fc93afd4522c282eda/src/fmu/dataio/_models/fmu_results/fmu_results.py#L48, examples are modified and a new schema for 0.11.0 is created.
The same happens when changing from 0.10.0 to 0.10.1.

However, when specifying --test --diff, the examples are still modified but no new schema is written.

It may be a good idea to go over the various options and mix of options, maybe reconsider the naming of the options, and ensure that the behaviour is as expected.

[mferrera]

When specifying --diff, it is expected that no file should be created or modified.

That's a reasonable expectation, I guess, consider e.g. git diff. My intention with --diff was just to print out what changes have occurred for a quick QC while making them rather than having it be a follow-up step