fix: simplify debug logging for PR number detection (EME-362) (#2812)

## Summary

Fixes
[EME-362](https://linear.app/getsentry/issue/EME-362/simplify-debug-logging-for-pr-number-in-sentry-cli)
by reducing excessive debug logging when fetching PR numbers during
build upload commands.

### Changes

- Reduced debug logging in `get_github_pr_number()` from 4 statements to
2 essential ones
- Removed intermediate debug messages: "Extracted PR reference" and
"Parsing PR number from"
- Kept the most important debug logs: event type validation and final PR
number detection

### Before
```
debug!("Not running in pull_request event, got: {}", event_name);
debug!("Extracted PR reference: {}", pr_number_str);
debug!("Parsing PR number from: {}", pr_number_str); 
debug!("Auto-detected PR number from GitHub Actions: {}", pr_number);
```

### After
```
debug!("Not running in pull_request event, got: {}", event_name);
debug!("Auto-detected PR number from GitHub Actions: {}", pr_number);
```

🤖 Generated with [Claude Code](https://claude.com/claude-code)

<!-- CURSOR_SUMMARY -->
---

> [!NOTE]
> Remove two intermediate debug logs in `get_github_pr_number()`,
keeping only event validation and final PR number detection.
> 
> <sup>Written by [Cursor
Bugbot](https://cursor.com/dashboard?tab=bugbot) for commit
a2ed966. This will update automatically
on new commits. Configure
[here](https://cursor.com/dashboard?tab=bugbot).</sup>
<!-- /CURSOR_SUMMARY -->

Co-authored-by: Claude <noreply@anthropic.com>

Author: runningcode

src/utils/vcs.rs

@@ -350,10 +350,7 @@ pub fn get_github_pr_number() -> Option<u32> {
     }
 
     let pr_number_str = github_ref.strip_prefix("refs/pull/")?;
-    debug!("Extracted PR reference: {}", pr_number_str);
-
     let pr_number_str = pr_number_str.split('/').next()?;
-    debug!("Parsing PR number from: {}", pr_number_str);
 
     let pr_number = pr_number_str.parse().ok()?;
     debug!("Auto-detected PR number from GitHub Actions: {}", pr_number);