Rewrite tests to not depend on currently broken dblp dataset

[Padarn]

This PR changes tests that were using the dblp as it seems to be currently broken.

[codecov]

Codecov Report

Merging #5250 (bac29c1) into master (fd77f03) will decrease coverage by 0.01%.
The diff coverage is n/a.

❗ Current head bac29c1 differs from pull request most recent head 3d9f402. Consider uploading reports for the commit 3d9f402 to get more accurate results

@@            Coverage Diff             @@
##           master    #5250      +/-   ##
==========================================
- Coverage   83.17%   83.15%   -0.02%     
==========================================
  Files         337      337              
  Lines       18574    18574              
==========================================
- Hits        15448    15445       -3     
- Misses       3126     3129       +3     

Impacted Files	Coverage Δ
torch_geometric/loader/hgt_loader.py	90.56% <0.00%> (-3.78%)	⬇️
torch_geometric/data/dataset.py	96.80% <0.00%> (-0.80%)	⬇️
torch_geometric/nn/pool/sag_pool.py	100.00% <0.00%> (ø)

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