[BUG REPORT] --date argument doesn't validate dates

For example, the following command accepts an invalid month "Dx" and an invalid year "20221" and sets the month to "Apr" and the year to "2020".

Yuri

$ git commit --amend --no-edit --date "Mon 20 Dx 20221 20:19:19 PST"
[master 668e255] Initial
  Date: Mon Apr 20 20:19:19 2020 -0700
  1 file changed, 1 insertion(+)
  create mode 100644 File
[yuri@yv /usr/home/yuri/github/git-date]$ git log
commit 668e255b54d08ed898e6d44f19954b2116d5a56c (HEAD -> master)
Author: Yuri <yuri@rawbw.com>
Date:   Mon Apr 20 20:19:19 2020 -0700

     Initial