Update path to app.bicep in tutorial_test.go (#6449)

# Description

Update path to app.bicep in radius repo per recent updates to samples
repo structure

## Type of change
- This pull request is a minor refactor, code cleanup, test improvement,
or other maintenance task and doesn't change the functionality of Radius
#6448

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Fixes: #6448

## Auto-generated summary

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### <samp>🤖 Generated by Copilot at 60a7572</samp>

### Summary
🚚📁🛠️

<!--
1. 🚚 This emoji can be used to indicate that a file or folder was moved
to a different location, as in this case where the template path was
updated to reflect the new location of the demo app.bicep file.
2. 📁 This emoji can be used to indicate that a file or folder was added,
modified, or deleted, as in this case where the samples directory was
restructured and the demo app.bicep file was relocated under it.
3. 🛠️ This emoji can be used to indicate that a file or folder was
fixed, improved, or updated, as in this case where the template path was
updated to match the new location of the demo app.bicep file and avoid
any errors or inconsistencies.
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Updated the template path in a functional test to match the new samples
layout. This ensures the test can find the `app.bicep` file for the
tutorial scenario.

> _`demo app.bicep`_
> _moved to samples directory_
> _a fresh spring cleaning_

### Walkthrough
* Update the template path in the tutorial test to match the new
location of `app.bicep` under the `samples` directory
([link](https://github.com/radius-project/radius/pull/6449/files?diff=unified&w=0#diff-a6eb33222335c5ca5618a71aa2c65413c4baafa31c91ed3523dd19ea43839a4eL63-R63))