test: Fix from-guessing to actually span Received headers over multiple lines

test: Fix from-guessing to actually span Received headers over multiple lines

The intent was always to make these Received headers span multiple
lines. But the escapes were causing the shell to ignore the newlines,
so that the result instead was long Received headers on a single line
each.

Fixing the intent here doesn't actually change the test-suite results
at all.