chore: Fix path for notebook test files in gitignore

[ppruthi]

Summary

Fixes relative path where notebook test files (*.py & *.txt) that are generated as a part of code compilation that should be ignored by git as these are runtime generated files that should not be checked in.

Tests

Made sure that with the changes, even after running sbt setup the notebook/**/*.py files don't show up on git status as untracked files that confuses the end user.

sbt setup && git status WITHOUT these changes:

 git status
On branch foobar
Your branch is up to date with 'origin/master'.

Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git restore <file>..." to discard changes in working directory)
        modified:   .gitignore

Untracked files:
  (use "git add <file>..." to include in what will be committed)
        notebooks/features/classification/Classification - Adult Census with Vowpal Wabbit.py
        notebooks/features/classification/Classification - Adult Census.py
        notebooks/features/classification/Classification - Before and After SynapseML.py
        notebooks/features/classification/Classification - Twitter Sentiment with Vowpal Wabbit.py
        notebooks/features/classification/ClassificationAdultCensus.py
        ...

sbt setup && git status WITH these changes:

$ git status
On branch user/ppruthi/foobar
nothing to commit, working tree clean

Dependency chances

None

AB#1758124