fix: add ECMAscript module

_Ideally_, we would just want to export it as ECMAscript module.

For now, to support both, we can use a shared JSON file.

It would be nice to use the `import cfg from "./config.js" assert { "json" };` but
that is experimental.

config.js

 // eslint-disable-next-line unicorn/prefer-module
-module.exports = {
-	branches: [
-		'+([0-9])?(.{+([0-9]),x}).x',
-		'stable',
-		{
-			name: 'beta',
-			prerelease: true,
-		},
-		{
-			name: 'alpha',
-			prerelease: true,
-		},
-	],
-};
+const cfg = require('./config.json');
+
+// eslint-disable-next-line unicorn/prefer-module
+module.exports = cfg;

config.json

+{
+	"branches": [
+		"+([0-9])?(.{+([0-9]),x}).x",
+		"stable",
+		{
+			"name": "beta",
+			"prerelease": true
+		},
+		{
+			"name": "alpha",
+			"prerelease": true
+		}
+	]
+}

config.mjs

+// eslint-disable-next-line import/order
+import {createRequire} from 'node:module';
+
+const require = createRequire(import.meta.url);
+const cfg = require('./config.json');
+
+export default cfg;

package.json

@@ -3,11 +3,14 @@
   "version": "0.0.0",
   "description": "A `semantic release` configuration for alpha, beta and stable release channels.",
   "exports": {
+    "import": "./config.mjs",
     "require": "./config.js"
   },
   "main": "config.js",
+  "modules": "config.mjs",
   "files": [
-    "config.js"
+    "config.js",
+    "config.mjs"
   ],
   "scripts": {
     "lint": "xo",

test/integration.test.mjs

+import test from 'ava';
+
+test('Can load the ECMAscript module', async t => {
+	const {default: {branches}} = await import('../config.mjs');
+
+	t.is(branches.length, 4);
+});