tests: more automated quote adjustment

Relax initial regexp to match more instances, but add a
filter to avoid some invalid conversions.  Run this:

git grep -l "\`[^']*'" tests | xargs perl -pi -e '$q=q"'\''";' \
  -e '$q="$q\\$q$q"; /(= ?\`|\`expr|\`echo|\Q$q\E)/ and next;' \
  -e ' s/\`([^'\''"]*?'\'')/'\''$1/g'
The last disjunct in the above (...) filter is to exempt
any line that contains this string: '\''
With quoting like that, converting a ` to ' is likely to cause trouble,
so we'll handle those manually.  Here are three examples where
the exemption is required:

  *': `link-to-dir/'\'': hard link not allowed for directory'*) ;;
  printf 'creating file `%s'\''\n' $f
  'mv: inter-device move failed: `%s'\'' to `%s'\'';'\

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/misc/test-diag b/tests/misc/test-diag
index c6e15cf47..9c0ce227f 100755
--- a/tests/misc/test-diag
+++ b/tests/misc/test-diag
@@ -27,7 +27,7 @@ my $prog = "$ENV{abs_top_builddir}/src/test";
 my @Tests =
     (
      # In coreutils-5.93, this diagnostic lacked the newline.
-     ['o', '-o arg', {ERR => "test: extra argument `-o'\n"},
+     ['o', '-o arg', {ERR => "test: extra argument '-o'\n"},
       {ERR_SUBST => 's!^.*:!test:!'},
       {EXIT => 2}],
     );