Security: file name restriction (#2768)

# Description of Changes

This PR updates the `check_properties.yml` workflow to refine the
file-matching regex for properties files.

### **What was changed:**
- Modified the regex used in two locations:
  1. In the GitHub CLI (`gh`) command to filter changed files:
     ```diff
     - '^src/main/resources/messages_[a-zA-Z_]+\.properties$'
+
'^src/main/resources/messages_[a-zA-Z_]{2}_[a-zA-Z_]{2,7}\.properties$'
     ```
  2. In the code to match relevant property files:
     ```diff
     - /^src\/main\/resources\/messages_[a-zA-Z_]+\.properties$/
+
/^src\/main\/resources\/messages_[a-zA-Z_]{2}_[a-zA-Z_]{2,7}\.properties$/
     ```

### **Why the change was made:**
- The previous regex matched any property files with loosely defined
patterns, including invalid or unintended formats.
- The updated regex ensures stricter matching of valid locale patterns:
  - Locale codes in the format `xx_XX` where:
    - `xx` represents a 2-character language code.
    - `XX` represents a 2-7 character region code.

### **Challenges encountered:**
- Ensuring compatibility across both the GitHub CLI command.
- Avoiding edge cases where valid property files might be excluded
unintentionally.

Closes # (issue_number)

---

## Checklist

### General

- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [x] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md)
(if applicable)
- [x] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md)
(if applicable)
- [x] I have performed a self-review of my own code
- [x] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [x] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/DeveloperGuide.md#6-testing)
for more details.

.github/workflows/check_properties.yml

@@ -58,7 +58,7 @@ jobs:
         run: |
           echo "Fetching PR changed files..."
           echo "Getting list of changed files from PR..."
-          gh pr view ${{ steps.get-pr-data.outputs.pr_number }} --json files -q ".files[].path" | grep -E '^src/main/resources/messages_[a-zA-Z_]+\.properties$' > changed_files.txt # Filter only matching property files
+          gh pr view ${{ steps.get-pr-data.outputs.pr_number }} --json files -q ".files[].path" | grep -E '^src/main/resources/messages_[a-zA-Z_]{2}_[a-zA-Z_]{2,7}\.properties$' > changed_files.txt # Filter only matching property files
 
       - name: Determine reference file test
         id: determine-file
@@ -99,7 +99,7 @@ jobs:
             // Filter for relevant files based on the PR changes
             const changedFiles = files
               .map(file => file.filename)
-              .filter(file => /^src\/main\/resources\/messages_[a-zA-Z_]+\.properties$/.test(file));
+              .filter(file => /^src\/main\/resources\/messages_[a-zA-Z_]{2}_[a-zA-Z_]{2,7}\.properties$/.test(file));
 
             console.log("Changed files:", changedFiles);