Fix: Expand tilde (~) in home directory paths for GTSRB dataset

[cynagenautes]

Description

This PR fixes an issue where the GTSRB dataset fails to recognize existing data when the root path contains a tilde (~) for the home directory.

Problem

Within torchvision/datasets/gtsrb.py, due to the root path not being correctly inherited from the VisionDataset class, pathlib.Path failed to automatically expand a path containing a tilde (e.g., ~/data) into its corresponding absolute home directory path (e.g., /home/username/data). Consequently, the _check_exists() method would incorrectly return False even when the dataset was already present, leading to superfluous downloads or runtime errors.

This issue was not observed in other classes, such as OxfordIIITPet, which correctly inherit and utilize the root path from the VisionDataset class.

Changes

• Rewrite to self.root to ensure proper inheritance from the VisonDataset class.
• This ensures that paths like ~/data/gtsrb are correctly resolved to absolute paths

[pytorch-bot]

🔗 Helpful Links

🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/vision/9263

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