Minor change to make latest version of ESLint pass (microsoft#1048)

### Motivation and Context
The newer ESLint is better and now complains about unneeded non-null
operators (!)

### Description
Remove the now-superfluous instances of '!'

### Contribution Checklist
- [ ] The code builds clean without any errors or warnings
- [ ] The PR follows the [Contribution
Guidelines](https://github.com/microsoft/chat-copilot/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/chat-copilot/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [ ] All unit tests pass, and I have added new tests where possible
- [ ] I didn't break anyone :smile

webapp/package.json

@@ -43,7 +43,7 @@
     "prettier": "^3.3.2",
     "react-scripts": "^5.0.1",
     "serve": "^14.2.3",
-    "typescript": "5.4.5"
+    "typescript": "5.5.3"
   },
   "browserslist": {
     "production": [

webapp/src/components/chat/chat-list/ChatList.tsx

@@ -111,8 +111,8 @@ export const ChatList: FC = () => {
             if (conversations[b].lastUpdatedTimestamp === undefined) {
                 return -1;
             }
-            // eslint-disable-next-line  @typescript-eslint/no-non-null-assertion
-            return conversations[a].lastUpdatedTimestamp! - conversations[b].lastUpdatedTimestamp!;
+
+            return conversations[a].lastUpdatedTimestamp - conversations[b].lastUpdatedTimestamp;
         });
 
         // Add conversations to sortedConversations in the order of sortedIds.

webapp/yarn.lock

@@ -11576,10 +11576,10 @@ typedarray-to-buffer@^3.1.5:
   dependencies:
     is-typedarray "^1.0.0"
 
-typescript@5.4.5:
-  version "5.4.5"
-  resolved "https://registry.yarnpkg.com/typescript/-/typescript-5.4.5.tgz#42ccef2c571fdbd0f6718b1d1f5e6e5ef006f611"
-  integrity sha512-vcI4UpRgg81oIRUFwR0WSIHKt11nJ7SAVlYNIu+QpqeyXP+gpQJy/Z4+F0aGxSE4MqwjyXvW/TzgkLAx2AGHwQ==
+typescript@5.5.3:
+  version "5.5.3"
+  resolved "https://registry.yarnpkg.com/typescript/-/typescript-5.5.3.tgz#e1b0a3c394190838a0b168e771b0ad56a0af0faa"
+  integrity sha512-/hreyEujaB0w76zKo6717l3L0o/qEUtRgdvUBvlkhoWeOVMjMuHNHk0BRBzikzuGDqNmPQbg5ifMEqsHLiIUcQ==
 
 unbox-primitive@^1.0.2:
   version "1.0.2"