Invalid prisma version used in tests

[rostislav-simonik]

Currently, tests with the latest Prisma automatically install the Prisma matching caret version. But we are locking prisma by yarn.lock. It means that different Prisma version is used in tests for all PRs resulting from time to time in unnecessary failures if a given version is incompatible with nexus-prisma. We still will have dedicated renovate prisma upgrade PR where we can capture those issues, but it will be narrowed to a single, dedicated PR.