Quarantine flaky tests related to reftable migration

This MR quarantines the flaky test TestInterceptor - #6849

Logs:

        time="2025-07-24T06:04:22Z" level=info msg="transaction committed" transaction.commit_lsn=0000000000003 transaction.description="reftable migration"
        time="2025-07-24T06:04:22Z" level=info msg="migration successful for repository" migration_attempts=1 migration_latency=120.24135ms relative_path=@cluster/repositories/d4/73/2 storage_name=default
        time="2025-07-24T06:04:22Z" level=error msg="partition failed" error="apply log entry: update: apply operations: remove: remove /tmp/gitaly-2176759883/510013940/storages.d/default/@cluster/repositories/d4/73/2/refs/heads: directory not empty" partition_id=3 partition_state_directory=+gitaly/partitions/4e/07/3 storage=default
        time="2025-07-24T06:04:22Z" level=info msg="diskcache state change" component=gitaly.UnaryServerInterceptor correlation_id=01K0XGGS3K8CGX1DPYAA4TRJNK diskcache=4ec9d815-f46e-4dff-adb7-77c7157d567e grpc.meta.auth_version=v2 grpc.meta.deadline_type=none grpc.meta.method_operation=mutator grpc.meta.method_scope=repository grpc.meta.method_type=unary grpc.method=DeleteRefs grpc.request.fullMethod=/gitaly.RefService/DeleteRefs grpc.request.glProjectPath=gitlab-org/gitlab-test grpc.request.glRepository=project-1 grpc.request.repoPath=@cluster/repositories/d4/73/2 grpc.request.repoStorage=default grpc.service=gitaly.RefService grpc.start_time="2025-07-24T06:04:22.527" span.kind=server system=grpc test="TestInterceptor/reftable_migration=true"
        time="2025-07-24T06:04:22Z" level=error msg="finished unary call with code Internal" component=gitaly.UnaryServerInterceptor correlation_id=01K0XGGS3K8CGX1DPYAA4TRJNK error="begin transaction: transaction processing stopped" feature_flags="git_v250 gpg_signing ref_iterator reftable_migration snapshot_filter" grpc.code=Internal grpc.meta.auth_version=v2 grpc.meta.deadline_type=none grpc.meta.method_operation=mutator grpc.meta.method_scope=repository grpc.meta.method_type=unary grpc.method=DeleteRefs grpc.request.fullMethod=/gitaly.RefService/DeleteRefs grpc.request.glProjectPath=gitlab-org/gitlab-test grpc.request.glRepository=project-1 grpc.request.payload_bytes=94 grpc.request.repoPath=@cluster/repositories/d4/73/2 grpc.request.repoStorage=default grpc.response.payload_bytes=0 grpc.service=gitaly.RefService grpc.start_time="2025-07-24T06:04:22.527" grpc.time_ms=1.021 span.kind=server system=grpc test="TestInterceptor/reftable_migration=true"
        time="2025-07-24T06:04:22Z" level=error msg="partition failed" error="apply log entry: update: apply operations: remove: remove /tmp/gitaly-2176759883/510013940/storages.d/default/@cluster/repositories/d4/73/2/refs/heads: directory not empty" partition_id=3 partition_state_directory=+gitaly/partitions/4e/07/3 storage=default

Based on the logs, it appears the WAL entries for migration and mutator RPC operations are sometimes being applied out of order.