Import - fixes (#12569)

<img width="800" alt="Screenshot 2025-06-12 at 15 22 49"
src="https://github.com/user-attachments/assets/afaa4ef1-b16c-4c05-ba4a-d77ad2ccfa76"
/>


To test : 
- unselect an option on select/multi-select matching (matching step)
- match a mutli-select field with an other field

closes : https://github.com/twentyhq/core-team-issues/issues/1065
closes : https://github.com/twentyhq/core-team-issues/issues/1066

packages/twenty-front/src/modules/spreadsheet-import/utils/setSubColumn.ts

@@ -14,9 +14,16 @@ export const setSubColumn = <T>(
 ):
   | SpreadsheetMatchedSelectColumn<T>
   | SpreadsheetMatchedSelectOptionsColumn<T> => {
+  const shouldUnselectValue =
+    oldColumn.matchedOptions.find((option) => option.entry === entry)?.value ===
+    value;
+
   const options = oldColumn.matchedOptions.map((option) =>
-    option.entry === entry ? { ...option, value } : option,
+    option.entry === entry
+      ? { ...option, value: shouldUnselectValue ? undefined : value }
+      : option,
   );
+
   const allMatched = options.every(({ value }) => !!value);
   if (allMatched) {
     return {