Gas sanity checks

[AmeliaNadal]

Fixes #864 .

Depends on #931.

Before merging into dev-branch, please make sure that

• [x] the CHANGELOG.rst was updated.
• [x] new and adjusted code is formated using black and isort.
• [x] the Dataset-version is updated when existing datasets are adjusted.
• [x] the branch was merged into the continuous-integration/run-everything-over-the-weekend-branch.
• [x] the workflow is running successful in test mode. -> some checks work also in test mode but not all of them
• [ ] the workflow is running successful in Everything mode.

[IlkaCu]

If I understand it right this PR includes changes about the 100RE scenario which shouldn't be merged right now. Can you 'divide' this PR into a 'eGon2035' and a 'eGon100RE' part, where the first one does not depend on #931?

[AmeliaNadal]

If I understand it right this PR includes changes about the 100RE scenario which shouldn't be merged right now. Can you 'divide' this PR into a 'eGon2035' and a 'eGon100RE' part, where the first one does not depend on #931?

The sanity checks for gas need to be completed, so I would close this PR and create two new ones as you've suggested:

• https://github.com/openego/eGon-data/pull/1068: sanity checks for the neighbouring countries need to be added,
• for eGon100RE: I've created a new issue (https://github.com/openego/eGon-data/issues/1067), which has lower priority for now.