smoketest: add regression test for 'tinygo test ./...', see #2892

tests/testing/recurse has two directories with tests;
"make smoketest" now does "tinygo test ./..." in that directory
and fails if it does not run both directories' tests.

tests/testing/recurse/subdir/subdir_test.go

@@ -0,0 +1,6 @@
+package subdir
+
+import "testing"
+
+func TestSubdir(t *testing.T) {
+}

tests/testing/recurse/top_test.go

@@ -0,0 +1,6 @@
+package top
+
+import "testing"
+
+func TestTop(t *testing.T) {
+}