Add old_name field to AuditEntry

[lmartinking]

This field is used when a repository is renamed.

Fixes: #2844.

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[gmlewis]

Please run go generate ./... in the top of this repo and push (not force-push) the changes to this PR.
See CONTRIBUTING.md for details.

[lmartinking]

@gmlewis I've run the codegen, as well as rebased against main

[codecov]

Codecov Report

Merging #2843 (b185d31) into master (7e3bb17) will not change coverage.
The diff coverage is n/a.

@@ Coverage Diff @@## master #2843 +/- ##
=======================================
Coverage 98.06% 98.06% =======================================
Files 138 138 Lines 12318 12318 =======================================
Hits 12080 12080 Misses 162 162 Partials 76 76 

Files Changed	Coverage Δ
github/orgs_audit_log.go	100.00% <ø> (ø)

[gmlewis]

Thank you, @lmartinking !
LGTM.
Merging.