[3.17] main/git: security upgrade to 2.39.5

Several security issues have been found that were backported only to 2.39.x.

• https://github.com/git/git/blob/master/Documentation/RelNotes/2.39.0.txt
• https://github.com/git/git/blob/master/Documentation/RelNotes/2.39.4.txt
• https://github.com/git/git/blob/master/Documentation/RelNotes/2.39.5.txt

Fixes: #16449 (closed)