Bug with Concurrent Series Requests in DWH Manager: Requests Remain "Pending Approval"

A bug occurs when two series requests are scheduled simultaneously, and the later request is approved before the earlier one. Following the sequence below results in both requests remaining in a "pending approval" state, despite being approved:

**Steps to Reproduce**
1. Schedule Series Request xy1:
- Planned execution: 2.1.20xx
- Reference date: 1.1.20xx

2. Schedule Series Request xy2:
- Planned execution: 2.2.20xx
- Reference date: 1.2.20xx

3. In the DWH Manager:
- Approve Series Request xy2 first.
- Then approve Series Request xy1.

**Observed Behavior**
* Both requests remain displayed as "Pending Approval" even after being approved.
* Clinics encounter delays and are unable to execute the queries as expected.

**Workaround**
* Clinics can manually resolve this issue by selecting the affected requests and disabling the "Series Approval" tab. This allows the requests to proceed, and subsequent series requests seem to execute without issue.

**Acceptance Criteria**
* Requests should automatically update to "Approved" status upon approval, regardless of the order in which they are approved.