Fix some issues reported by lintian

Fix some issues reported by lintian

• Set upstream metadata fields: Bug-Database, Bug-Submit, Repository-Browse. (upstream-metadata-file-is-missing, upstream-metadata-missing-bug-tracking)
• Update standards version to 4.6.2, no changes needed. (out-of-date-standards-version)

These changes have no impact on the binary debdiff.

You can also view the diffoscope diff (unfiltered).

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