fix(deps): update dependency @google-cloud/datastore to v6

[renovate-bot]

This PR contains the following updates:

Package	Type	Update	Change
@google-cloud/datastore	dependencies	major	^5.0.0 -> ^6.0.0

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Release Notes

googleapis/nodejs-datastore

v6.0.0

Compare Source

⚠ BREAKING CHANGES

• The Datastore.projectId property has been removed, and replaced with an asynchronous getProjectid() method. The projectId cannot be determined synchronously, so the previous approach was to use a {{projectId}} string placeholder if the projectId had not yet been acquired. This made it difficult to know exactly when the property would be defined.
• The library now supports Node.js v10+. The last version to support Node.js v8 is tagged legacy-8 on NPM.

Features

• add async getProjectId method (#​657) (2a7e034)
• add options param to query#runStream (#​611) (7429c9d)
• drop node8 support (#​637) (7ef38c1)

Bug Fixes

• deps: update dependency @​google-cloud/projectify to v2 (#​626) (27fa23f)
• deps: update dependency @​google-cloud/promisify to v2 (#​625) (1d64bc1)
• remove eslint, update gax, fix generated protos, run the generator (#​644) (fcc5309)
• deps: update dependency @​grpc/grpc-js to v0.7.1 (#​615) (3e83981)
• identify propertyName (#​614) (3635e13)
• missing await in rollback (#​671) (7cb353e)
• deps: update dependency @​grpc/grpc-js to v0.7.4 (#​620) (1d36be1)
• deps: update dependency @​grpc/grpc-js to v0.7.8 (#​638) (a98ee1a)
• regenerate files and fixed formatting, lint (#​664) (34e9135)
• support request params {key} with no =value (#​660) (1faba1f)
• trim the dependency tree (#​651) (1fd412e)
• deps: update dependency @​grpc/grpc-js to v0.7.9 (#​645) (04b2ab2)
• deps: update dependency google-auth-library to v6 (#​628) (eb5f87b)

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