Add proper error messages in __check_input__()

[modanesh]

Added proper and relative error messages while checking the edge_index in __check_input__() function.

[codecov]

Codecov Report

Merging #5042 (3653757) into master (6ed5caf) will decrease coverage by 1.90%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #5042      +/-   ##
==========================================
- Coverage   84.74%   82.83%   -1.91%     
==========================================
  Files         331      331              
  Lines       18162    18158       -4     
==========================================
- Hits        15391    15041     -350     
- Misses       2771     3117     +346     

Impacted Files	Coverage Δ
torch_geometric/nn/conv/message_passing.py	98.84% <100.00%> (ø)
torch_geometric/nn/models/dimenet_utils.py	0.00% <0.00%> (-75.52%)	⬇️
torch_geometric/nn/models/dimenet.py	14.51% <0.00%> (-53.00%)	⬇️
torch_geometric/nn/conv/utils/typing.py	81.25% <0.00%> (-17.50%)	⬇️
torch_geometric/profile/profile.py	32.94% <0.00%> (-15.30%)	⬇️
torch_geometric/nn/inits.py	67.85% <0.00%> (-7.15%)	⬇️
torch_geometric/nn/resolver.py	88.00% <0.00%> (-6.00%)	⬇️
torch_geometric/transforms/add_self_loops.py	94.44% <0.00%> (-5.56%)	⬇️
torch_geometric/io/tu.py	93.90% <0.00%> (-2.44%)	⬇️
torch_geometric/transforms/virtual_node.py	97.56% <0.00%> (-2.44%)	⬇️
... and 9 more

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[rusty1s]

Thanks!

[rusty1s]

Can we fix the linting error reported by the CI?