In git 2.48.1, the `git update-ref` subcommand no longer correctly
updates the reflog in some cases. Specifically, it appears that the
`old_oid` field will not be updated when modifying a branch referenced
by another symbolic ref (e.g. HEAD). This doesn't break the `git
reflog` subcommand, but does break references like `HEAD@{1}`, which
appear to read the `old_oid` field.
STR (in a fresh directory):
```
git init -b main
git commit --allow-empty -m "A"
git commit --allow-empty -m "B"
git update-ref -m "reason" refs/heads/main HEAD~ HEAD
```
Expected Result:
```
$ git rev-parse HEAD@{1}
70d9116663eee9f01065c3a6d8984b1dea661f20
$ cat .git/logs/HEAD
0000000000000000000000000000000000000000
17dd31aaf89190a36b8d04136a1a0f83fb37da4c AUTHOR <EMAIL> TIME commit
(initial): A
17dd31aaf89190a36b8d04136a1a0f83fb37da4c
70d9116663eee9f01065c3a6d8984b1dea661f20 AUTHOR <EMAIL> TIME commit:
B
70d9116663eee9f01065c3a6d8984b1dea661f20
17dd31aaf89190a36b8d04136a1a0f83fb37da4c AUTHOR <EMAIL> TIME reason
```
The `old_oid` field for the reflog entry added by `git update-ref` is
present, and correctly initialized. This was the case prior to git
2.48.
Actual Result:
```
$ git rev-parse HEAD@{1}
warning: log for ref HEAD unexpectedly ended on TIME
17dd31aaf89190a36b8d04136a1a0f83fb37da4c
$ cat .git/logs/HEAD
0000000000000000000000000000000000000000
17dd31aaf89190a36b8d04136a1a0f83fb37da4c AUTHOR <EMAIL> TIME commit
(initial): A
17dd31aaf89190a36b8d04136a1a0f83fb37da4c
70d9116663eee9f01065c3a6d8984b1dea661f20 AUTHOR <EMAIL> TIME commit:
B
0000000000000000000000000000000000000000
17dd31aaf89190a36b8d04136a1a0f83fb37da4c AUTHOR <EMAIL> TIME reason
```
The `old_oid` field is empty (all zeroes). This is only the case in
derived reflogs (in this case .git/logs/HEAD). The reflog for
refs/heads/main appears to be updated correctly.
