Reorder tests to not use the same number (#2947)

Distinct numbers make re-running individual tests easier by helping with
tab-completion.

Completeness verified using:
% for i in $(seq 0 600)
do
  files=$(ls testcases/t/$(printf "%03d" $i)-*.t 2>&- | wc -l)
  [ "$files" != "0" ] && [ "$files" != "1" ] && echo "clash: $i"
done

testcases/t/273-regress-focus-toggle.t

@@ -0,0 +1,30 @@
+#!perl
+# vim:ts=4:sw=4:expandtab
+#
+# Please read the following documents before working on tests:
+# • http://build.i3wm.org/docs/testsuite.html
+#   (or docs/testsuite)
+#
+# • http://build.i3wm.org/docs/lib-i3test.html
+#   (alternatively: perldoc ./testcases/lib/i3test.pm)
+#
+# • http://build.i3wm.org/docs/ipc.html
+#   (or docs/ipc)
+#
+# • http://onyxneon.com/books/modern_perl/modern_perl_a4.pdf
+#   (unless you are already familiar with Perl)
+#
+# Regression: Checks if i3 still lives after using 'focus mode_toggle' on an
+# empty workspace. This regression was fixed in
+# 0848844f2d41055f6ffc69af1149d7a873460976.
+#
+use i3test;
+use v5.10;
+
+my $tmp = fresh_workspace;
+
+cmd 'focus mode_toggle';
+
+does_i3_live;
+
+done_testing;