Add unit test for FileInfo.getFormattedFileSize (#3132)

# Description of Changes

Add Unit Test for FileInfo.getFormattedFileSize

Closes #3089

---

## 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.

src/main/java/stirling/software/SPDF/utils/FileInfo.java

@@ -4,6 +4,7 @@ import java.nio.file.Path;
 import java.nio.file.Paths;
 import java.time.LocalDateTime;
 import java.time.format.DateTimeFormatter;
+import java.util.Locale;
 
 import lombok.AllArgsConstructor;
 import lombok.Data;
@@ -27,11 +28,11 @@ public class FileInfo {
     // Formats the file size into a human-readable string.
     public String getFormattedFileSize() {
         if (fileSize >= 1024 * 1024 * 1024) {
-            return String.format("%.2f GB", fileSize / (1024.0 * 1024 * 1024));
+            return String.format(Locale.US, "%.2f GB", fileSize / (1024.0 * 1024 * 1024));
         } else if (fileSize >= 1024 * 1024) {
-            return String.format("%.2f MB", fileSize / (1024.0 * 1024));
+            return String.format(Locale.US, "%.2f MB", fileSize / (1024.0 * 1024));
         } else if (fileSize >= 1024) {
-            return String.format("%.2f KB", fileSize / 1024.0);
+            return String.format(Locale.US, "%.2f KB", fileSize / 1024.0);
         } else {
             return String.format("%d Bytes", fileSize);
         }