po: Update translations to build with gettext 0.26

Gettext 0.26 validates format strings. In some cases before
the GRUB build process was converting newlines sequences (\n)
to (\<translated character>) which is invalid. Update the
impacted language sed script files to ensure newlines use
the correct escape sequence.

This avoids build errors such as:

  de@hebrew.po:8192: 'msgstr' is not a valid Shell printf format string, unlike 'msgid'. Reason: This escape sequence is invalid.

Fixes: https://savannah.gnu.org/bugs/?67353

Signed-off-by: Andrew Hamilton <adhamilt@gmail.com>
Reviewed-by: Vladimir Serbinenko <phcoder@gmail.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

po/greek.sed

@@ -106,3 +106,5 @@ s,%\([0-9]*\)ζυ,%\1zu,g
 s,%\([0-9]*\)ξ,%\1x,g
 s,%\([0-9]*\)λξ,%\1lx,g
 s,%\([0-9]*\)λλξ,%\1llx,g
+
+s,\\ν,\\n,g