fix(lib): correct the concat method in TokenizedStringFragments

The concat method was not properly updating `this.fragments` because `Array.prototype.concat` does not modify the original array in place. Changed the implementation to use `push` with the spread operator to correctly merge fragments.

packages/cdktf/lib/tokens/string-fragments.ts

@@ -87,7 +87,7 @@ export class TokenizedStringFragments {
   }
 
   public concat(other: TokenizedStringFragments): void {
-    this.fragments.concat(other.fragments);
+    this.fragments.push(...other.fragments);
   }
 
   /**