fix(longmt_eval): use valid 'Apache 2.0' license literal

[wprazuch]

What

resources_servers/longmt_eval/configs/longmt_eval.yaml and longmt_pg19.yaml set
license: Apache-2.0 (hyphen). That is not a valid DatasetConfig.license literal — the
allowed value is Apache 2.0 (with a space), which the sibling longmt_wmt24pp.yaml already
uses correctly. This aligns all three configs.

Loading either of the two affected configs through get_global_config_dict() currently raises
a pydantic ValidationError:

'Apache 2.0':  OK
'Apache-2.0':  REJECTED (ValidationError)

⚠️ This does not fully green the longmt_eval data-validation CI

While investigating the Test job failure that shows up on every open PR, I found two
separate issues in longmt_eval (added in #1458):

1. This PR — the invalid Apache-2.0 license literal (a latent config-parse bug).
2. Still outstanding — the Test job's data validation (_validate_data_single in cli.py)
   requires resources_servers/longmt_eval/data/example_metrics.json, but the server only ships
   example_rollouts_agent_metrics.json. The missing file is what actually reds the Test job
   for all PRs (it validates all 114 servers), e.g. on fix(config): actionable error for unknown server cross-references #1561.

@jeffwillette — could you regenerate and commit data/example_metrics.json for longmt_eval?
It comes from:

ng_prepare_data "+config_paths=[resources_servers/longmt_eval/configs/longmt_eval.yaml]" \
    +output_dirpath=data/longmt_eval \
    +mode=example_validation

That step needs the server's GPU/SEGALE/COMET environment, which is why it's best done on your
side. Happy to fold it into this PR or you can land it separately — whichever is easier.

Testing

Apache 2.0 validates against DatasetConfig; pre-commit clean (verified-flag + README hooks
pass with no changes).

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[wprazuch]

Superseded by #1559, which landed the identical license fix (Apache-2.0 → Apache 2.0 in both configs) and added the missing data/example_metrics.json that was the actual CI blocker. Closing — nothing left to do here. Thanks @jeffwillette!