fix(Find): When auth_context input is omitted, use a parseable fallback to avoid SyntaxError (#1720)

Fixes the following error (e.g. in
https://github.com/github-community-projects/continuous-ai-for-accessibility-scanner-demo/actions/runs/18316400478/job/52157716701):

```
SyntaxError: Unexpected end of JSON input
    at JSON.parse (<anonymous>)
    at Module.default (file:///home/runner/work/continuous-ai-for-accessibility-scanner-demo/continuous-ai-for-accessibility-scanner-demo/.github/actions/find/dist/index.js:8:35)
```

This is basically the same issue I caught in
github-community-projects/continuous-ai-for-accessibility-scanner#1707 (comment),
only I didn’t catch it here (until now).

Author: smockle

.github/actions/find/src/index.ts

@@ -8,7 +8,7 @@ export default async function () {
   const urls = core.getMultilineInput("urls", { required: true });
   core.debug(`Input: 'urls: ${JSON.stringify(urls)}'`);
   const authContextInput: AuthContextInput = JSON.parse(
-    core.getInput("auth_context", { required: false }) ?? "{}"
+    core.getInput("auth_context", { required: false }) || "{}"
   );
   const authContext = new AuthContext(authContextInput);