Aiida-export-migration-tests

Minor fixes due to changes in [aiida-core](https://github.com/aiidateam/aiida_core).

Folder `fixtures` changes name to `archives` to match the same change happening for aiida-core.
The simple AiiDA export archives in aiida-core representing the different export versions have changed names:

- `export_v0.1_no_UPF.aiida` -> `export_v0.1_simple.aiida`
- `export_v0.2_no_UPF.aiida` -> `export_v0.2_simple.aiida`
- `export_v0.3_no_UPF.aiida` -> `export_v0.3_simple.aiida`
- `export_v0.4_no_UPF.aiida` -> `export_v0.4_simple.aiida`

A change in the conversion message included in `metadata.json` files, when a migration has been successfully performed, introduces the version of AiiDA into the message. In order to have the tests be version-agnostic, the `conversion_info` key has to be handled specially in the relevant tests.
When migrating an archive, it is asserted that the correct conversion message appears in the migrated archive, and the `conversion_info` item is then popped from both the migrated archive and the archive imported for comparison.

Update repository with export archive for export versions 0.6 and 0.7.
These files are named differently, having the suffix `_manual`, since they were not produced properly, through a new workflow run in AiiDA.
Instead, the export file `export_v0.4.aiida` has been the unpacked, updated manually, and repacked.

The file `export_v0.5.aiida` has also been made this way, and will therefore have its name changed accordingly.

*New files*:

- `export_v0.5_manual.aiida` (only the filename has been altered)
- `export_v0.6_manual.aiida`
- `export_v0.7_manual.aiida`

Update version number of this repository to reflect the current `EXPORT_VERSION` in `aiida_core`.
The version number is now as follows: `<EXPORT_VERSION>.<patch>`

Implement initial change related to the update of `EXPORT_VERSION` from 0.4 to 0.5:

- _Migration [0034](https://github.com/aiidateam/aiida_core/blob/b8eaffca3c448d1242eded845aa118b4bc1ae1a9/aiida/backends/djsite/db/migrations/0034_drop_node_columns_nodeversion_public.py)_: Remove fields/columns `"nodeversion"` and `"public"` from the `DbNode` model.
- _Migration [0036](https://github.com/aiidateam/aiida_core/blob/af56391b5bdfbbc3e1d0ef7d36180128bb28f695/aiida/backends/djsite/db/migrations/0036_drop_computer_transport_params.py)_: Remove field/column `"transport_params"` from the `DbComputer` model.

_Note_: The newly created `export_v0.5.aiida` under `/aiida-export-migration-tests/archives` is _not_ actually created from an AiiDA workflow, but instead a migration of `export_v0.4.aiida`.
This is because the changes between the versions are insignificant for the outcome of the workflow, and that only very minor changes have occurred.

**AiiDA version**: _To be released_

Update repository with export archive for export version 0.9.
The file follows the naming of previous export version files having the suffix `_manual`, since it was not produced properly, i.e., through a new workflow run in AiiDA.
Instead, the export file `export_v0.8_manual.aiida` has been the unpacked, updated manually, and repacked.
This means the latest "proper" export file is `export_v0.4.aiida`.

Changes are expected to be released with AiiDA version 1.2.0.

*New file*: `export_v0.9_manual.aiida`