tests: enclose $PERL_PATH in double quotes

Otherwise it will be split at a space after "Program" when it is set
to "\\Program Files\perl" or something silly like that.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t4029-diff-trailing-space.sh

@@ -27,7 +27,7 @@ test_expect_success \
      git config --bool diff.suppressBlankEmpty true &&
      git diff f > actual &&
      test_cmp exp actual &&
-     $PERL_PATH -i.bak -p -e "s/^\$/ /" exp &&
+     "$PERL_PATH" -i.bak -p -e "s/^\$/ /" exp &&
      git config --bool diff.suppressBlankEmpty false &&
      git diff f > actual &&
      test_cmp exp actual &&