Use .datax for `make test`, not .data

Looking for the .data file doesn't work in out-of-tree builds. Use the
.datax file instead. `make clean` removes all .datax files, so this resolves
the issue of executables not present on the current branch being left behind
after a branch change followed by a `make clean`.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
diff --git a/tests/scripts/run-test-suites.pl b/tests/scripts/run-test-suites.pl
index 8a5bb93..cedc0bf 100755
--- a/tests/scripts/run-test-suites.pl
+++ b/tests/scripts/run-test-suites.pl
@@ -50,10 +50,10 @@
            'verbose|v:1' => \$verbose,
           ) or die;
 
-# All test suites = executable files derived from a .data file.
+# All test suites = executable files with a .datax file.
 my @suites = ();
-for my $data_file (glob 'suites/test_suite_*.data') {
-    (my $base = $data_file) =~ s#^suites/(.*)\.data$#$1#;
+for my $data_file (glob 'test_suite_*.datax') {
+    (my $base = $data_file) =~ s/\.datax$//;
     push @suites, $base if -x $base;
     push @suites, "$base.exe" if -e "$base.exe";
 }