Fix some issues reported by lintian

Fix some issues reported by lintian

• debian/copyright: use spaces rather than tabs to start continuation lines. (tab-in-licence-text)
• Set upstream metadata fields: Bug-Database, Repository, Repository-Browse. (upstream-metadata-file-is-missing)
• Set upstream metadata fields: Bug-Submit.

This merge proposal was created automatically by the Janitor bot.

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Build and test logs for this branch can be found at https://janitor.debian.net/lintian-fixes/pkg/python-jsonschema/40320cdf-941e-4200-a821-6cf844c8e0eb.

These changes have no impact on the binary debdiff.

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