[3.13] gh-85012: Properly reset msgctxt when compiling messages with msgfmt (GH-130525) (GH-131205)

Add also human-readable snapshots for tests.
(cherry picked from commit 7ea6e88eb490635518c63c3305c03baf3e151555)

Co-authored-by: Tomas R <tomas.roun8@gmail.com>