fix(compiler): don't overwrite missingTranslation's value in JIT (#19952)

packages/compiler/test/config_spec.ts

@@ -0,0 +1,19 @@
+/**
+ * @license
+ * Copyright Google Inc. All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.io/license
+ */
+
+import {MissingTranslationStrategy} from '@angular/core';
+import {CompilerConfig} from '../src/config';
+
+export function main() {
+  describe('compiler config', () => {
+    it('should set missing translation strategy', () => {
+      const config = new CompilerConfig({missingTranslation: MissingTranslationStrategy.Error});
+      expect(config.missingTranslation).toEqual(MissingTranslationStrategy.Error);
+    });
+  });
+}