Only copy source code to test notebook if install URI not supplied

[iansrobinson]

Issue #, if available:

Description of changes:

By default, the integration tests copy the lexical graph source to the test notebook. When the tests run, they use this local version of the toolkit.

With this change, if a --lexical-graph-install parameter is supplied, the source will not be copied to the notebook. This ensures the tests run against the install supplied in the parameter.

For example:

sh build-tests.sh --test-file lexical.short

will run tests against the source code copied to the notebook, whereas

sh build-tests.sh --test-file lexical.short --lexical-graph-install graphrag-lexical-graph

will run the tests against the latest version of the toolkit from PyPi.

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