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-license-text)
• Set upstream metadata fields: Repository. (upstream-metadata-file-is-missing, upstream-metadata-missing-repository)

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Build and test logs for this branch can be found at https://janitor.debian.net/lintian-fixes/pkg/cgit/17e7a9da-2c9f-48c8-ba44-1e0a94b7c30c.

Debdiff

These changes affect the binary packages:

File lists identical (after any substitutions)

Control files of package cgit: lines which differ (wdiff format)

• Depends: libc6 (>= 2.28), liblua5.1-0, liblua5.1-0 (>= 5.1.5), zlib1g (>= 1:1.2.0)

No differences were encountered between the control files of package **cgit-dbgsym**

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