Fix snapcraft upload

[koppor]

This PR tries to fix upload to snapcraft.

Before this PR:

Run snapcore/action-publish@v1
  with:
    store_login: ***
    snap: jabref_5.2.376_amd64.snap
    release: edge
Publishing snap "jabref_5.2.376_amd64.snap"...
/snap/bin/snapcraft login --with /tmp/login-data-37F4mR/login.txt
Unexpected error when obtaining your account information.
Login failed.
Error: The process '/snap/bin/snapcraft' failed with exit code 1

See https://github.com/JabRef/jabref/runs/1605853743

• Change in CHANGELOG.md described (if applicable)
• Tests created for changes (if applicable)
• Manually tested changed features in running JabRef (always required)
• Screenshots added in PR description (for UI changes)
• Checked documentation: Is the information available and up to date? If not created an issue at https://github.com/JabRef/user-documentation/issues or, even better, submitted a pull request to the documentation repository.

[Siedlerchr]

@LyzardKing The snap seems to throw an error:

 The store was unable to accept this snap.
  - human review required due to 'allow-installation' constraint (interface attributes)
  - interface reference 'etc-opt-edge-native-messaging-jabref' not allowed. Please use one of: hostfs-mozilla-native-messaging-jabref, etc-opt-chrome-native-messaging-jabref, etc-chromium-native-messaging-jabref

[koppor]

Our SnapCraft build seems to have not worked since 2 months (think, it is related to #7056).

Now, I have following two reports:

• human review required due to 'allow-installation' constraint (interface attributes)
• interface reference 'etc-opt-edge-native-messaging-jabref' not allowed. Please use one of: hostfs-mozilla-native-messaging-jabref, etc-opt-chrome-native-messaging-jabref, etc-chromium-native-messaging-jabref

I will request the human review because of etc-opt-edge-native-messaging-jabref. I ask for it at https://forum.snapcraft.io/t/system-files-under-mozilla-native-messaging-hosts/13627/42?u=koppor.

[Siedlerchr]

I merge this, should not influence our waiting for manual review