Fix typos (#3214)

.github/PULL_REQUEST_TEMPLATE.md

@@ -8,7 +8,7 @@ Please feel free to remove inapplicable items for your PR.
 - [ ] Changes are complete (i.e. I finished coding on this PR)
 - [ ] All changes have test coverage
 - [ ] Code is well-documented
-- [ ] To the my best knowledge, examples are either not affected by this change,
+- [ ] To the best of my knowledge, examples are either not affected by this change,
       or have been fixed to be compatible with this change
 - [ ] Related issue is referred in this PR
 - [ ] If the PR is for a new model/paper, I've updated the example index [here](../examples/README.md).

tutorials/models/1_gnn/9_gat.py

@@ -29,7 +29,7 @@ One workaround is to simply average over all neighbor node features as described
 the research paper `GraphSAGE
 <https://www-cs-faculty.stanford.edu/people/jure/pubs/graphsage-nips17.pdf>`_.
 However, `Graph Attention Network <https://arxiv.org/abs/1710.10903>`_ proposes a
-different type of aggregation. GAN uses weighting neighbor features with feature dependent and
+different type of aggregation. GAT uses weighting neighbor features with feature dependent and
 structure-free normalization, in the style of attention.
 """
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