Removes unused `bun install` steps from two CI workflow files (`ci.yml` and `pr-checks.yml`), cleaning up the test-shards job configuration. Fusion-Task-Id: FN-4105
Removes unused `bun install` steps from two CI workflow files (`ci.yml` and `pr-checks.yml`), cleaning up the test-shards job configuration. Fusion-Task-Id: FN-4105