Log hashes of local branches when deleting them

[stefanhaller]

This makes it easier to recover them if they were deleted accidentally.

We only do this for local branches for now, we don't bother for remote branches; it would be trickier there, because the branch on the server might not actually point to the same hash as our local remote tracking branch does.

Fixes #2468.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 0 complexity · 0 duplication

Metric	Results
Complexity	0
Duplication	0

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🟢 Coverage 100.00% diff coverage

Metric	Results
Coverage variation	Report missing for 4c2c0ce1
Diff coverage	✅ 100.00% diff coverage

View coverage diff in Codacy

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (4c2c0ce)	Report Missing	Report Missing	Report Missing
Head commit (e4309f1)	61722	53692	86.99%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#5441)	20	20	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

¹ Codacy didn't receive coverage data for the commit, or there was an error processing the received data. Check your integration for errors and validate that your coverage setup is correct.

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