test: replace $PWD with YYY in emacs & emacs-show tests

test: replace $PWD with YYY in emacs & emacs-show tests

When executed command line is written to *Notmuch errors* buffer,
shell-quote-argument will backslash-escape any char that is not in
"POSIX filename characters" (i.e. matching "[^-0-9a-zA-Z_./\n]").

Currently in two emacs tests shell has expanded $PWD as part of
emacs variable, which will later be fed to #'shell-quote-argument
and finally written to ERROR file. If $PWD contained non-POSIX
filename characters, data in ERROR file will not match $PWD when
later comparing in shell. Therefore, in these two particular cases
the escaped $PWD is replaced with YYY in ERROR file and expected
content is adjusted accordingly.