Use query variables instead of f-strings in swh-graphql tests

They would make tests easier to read/write (no double-escaping of {}) and reuse (just need to change variables)

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Migrated from T4306 (view on Phabricator)

mentioned in merge request !25 (closed)

marked this issue as related to #4261 (closed)

added GraphQL API priority:Low labels

assigned to @jayeshv

mentioned in commit 04b81ece

mentioned in commit 2c457bf0

closed

mentioned in merge request !17 (closed)