Odoo Support says that this is not a bug, and it is the intended behavior of the Gmail Plugin.  I don't agree but that is what they said.  They said that I should use Automated Actions to stop the plugin from creating duplicate contacts, or use Data Cleaning, or manually Merge the duplicate contacts.

The best thing would be to either create an Automated Action within Odoo that stops a duplicate from being made. Here is a link to the documentation to set up an Automated Action:

https://www.odoo.com/documentation/16.0/applications/productivity/studio/automated_actions.html?highlight=automated%20action

Another Option may be to install the Data Cleaning App from the Apps page.

For the Duplicates you can also Merge them so there is only one or Archive the Duplicates.