Usually the user is a maintainer using split brain, and we should rely
on their own gbp configuration to specify the right check.
Closes:#841100.
+ * split brain cache: Fix a wrong implicit reference to $_.
+ Closes:#841383.
+ * split brain cache: Make sure to write reflog entries for cache updates
+ even if the eventual tree (and therefore commit) is the same.
+ Otherwise, after updating dgit, the cache might have the right answer
+ but not be refreshed even by a build.
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