l10n: git.pot: v2.6.0 round 2 (3 improvements)

Introduce three i18n improvements from the following commits:

* tag, update-ref: improve description of option "create-reflog"
* pull: don't mark values for option "rebase" for translation
* show-ref: place angle brackets around variables in usage string

Signed-off-by: Jiang Xin <[email protected]>

Author: jiangxin