test(ui5-select, ui5-multi-combobox): re-enable flaky form submission tests

[nnaydenow]

The following tests were temporarily skipped in #13656 due to flakiness on CI:

• File: packages/main/cypress/specs/FormSupportSubmission.cy.tsx
• Test (MultiComboBox): Form submission with Enter key > fires submit on second Enter after selection is confirmed
  • Error: expected submit to have been called exactly once, but it was never called
• Test (Select): Form submission with Enter key > Select > doesn't submit form when Enter is pressed
  • Error: expected '<ui5-select>' to be 'focused'