chore(observability-map): declare the ES2020 lib the tests already need

The tests call String.prototype.matchAll, an ES2020 library feature, while
`lib` said ES2019. Typecheck passed anyway because @types/node v24 declares
`/// <reference lib="es2020" />`, so the program already contained es2020.
No behaviour changes; the declaration now states the requirement instead of
resting on a transitive reference.

Author: 1stvamp

internal-packages/observability-map/tsconfig.json

@@ -1,7 +1,11 @@
 {
   "compilerOptions": {
     "target": "ES2019",
-    "lib": ["ES2019"],
+    // ES2020 rather than the ES2019 most sibling packages use, because the tests call
+    // String.prototype.matchAll. It already resolved: @types/node carries a
+    // `/// <reference lib="es2020" />`, so the program had es2020 whatever this line said. Stating
+    // it here stops the requirement resting on a transitive reference from a types package.
+    "lib": ["ES2020"],
     "module": "ESNext",
     "moduleResolution": "Bundler",
     "esModuleInterop": true,