test: test Deno codepath on non-Deno platforms too

Author: ChALkeR

tests/single-byte.deno.test.cjs

@@ -0,0 +1,7 @@
+if (process.browser) {
+  const { test } = require('node:test')
+  test.skip('Deno tests')
+} else {
+  if (!globalThis.Deno) globalThis.Deno = true
+  require('./single-byte.test.js')
+}

tests/utf16.deno.test.cjs

@@ -0,0 +1,7 @@
+if (process.browser) {
+  const { test } = require('node:test')
+  test.skip('Deno tests')
+} else {
+  if (!globalThis.Deno) globalThis.Deno = true
+  require('./utf16.test.js')
+}