Fix ghost blocks

[fselmo]

What was wrong?

get_block methods were able to retrieve the pending block by number before it was added to the chain. This is misleading since the block has not yet been added to the chain. The pending block should only be retrieved via the block identifier pending.

How was it fixed?

• Change logic to only allow the pending block to be retrieved via the pending block identifier for get_block methods.
• Test for the above changes

To-Do:

• [x] Add entry to the release notes

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