Suggest improvements form drops the CVSS 3.1 vector when an advisory has both 3.1 and 4.0

[nikpivkin]

I used the "Suggest improvements for this vulnerability" form on GHSA-984m-rj28-8c6x to change the range of one entry. I did not touch the severity. But the pull request #9627 also removes the CVSS_V3 entry and keeps only CVSS_V4. Here is the part of its diff.

   "severity": [
-    {
-      "type": "CVSS_V3",
-      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N"
-    },
     {
       "type": "CVSS_V4",
       "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N"

The advisory has both vectors. The form has a "Severity" select with "Assess severity using CVSS v4" and one "Vector string" field, so it can hold only one vector. When I submit the form, the other vector is lost.

I expect the form to keep the CVSS 3.1 vector when I do not edit the severity.