Update angular monorepo to v20

Author: renovate[bot]

package.json

@@ -41,10 +41,10 @@
   },
   "homepage": "https://github.com/esm-bundle/angular__elements#readme",
   "devDependencies": {
-    "@angular/compiler": "15.2.10",
-    "@angular/compiler-cli": "15.2.10",
-    "@angular/core": "15.2.10",
-    "@angular/elements": "15.2.10",
+    "@angular/compiler": "20.3.6",
+    "@angular/compiler-cli": "20.3.6",
+    "@angular/core": "20.3.6",
+    "@angular/elements": "20.3.6",
     "@rollup/plugin-babel": "6.0.4",
     "concurrently": "8.2.2",
     "husky": "8.0.3",