[8.18] fix: [Platform:StackManagement:Kibana:Spaces] Assign roles to a space flyout announced incorrectly (#218576) (#218608)

# Backport

This will backport the following commits from `main` to `8.18`:
- [fix: [Platform:StackManagement:Kibana:Spaces] Assign roles to a space
flyout announced incorrectly
(#218576)](https://github.com/elastic/kibana/pull/218576)

<!--- Backport version: 9.6.6 -->

### Questions ?
Please refer to the [Backport tool
documentation](https://github.com/sorenlouv/backport)

<!--BACKPORT [{"author":{"name":"Alexey
Antonov","email":"alexwizp@gmail.com"},"sourceCommit":{"committedDate":"2025-04-17T18:52:56Z","message":"fix:
[Platform:StackManagement:Kibana:Spaces] Assign roles to a space flyout
announced incorrectly (#218576)\n\nCloses:
#218351\n\n**Description**\nWhen user clicks on assign new roles to a
space button, the resulting\nflyout gets announced incorrectly as \"you
are in a modal dialog...\"\nwhich doesn't give any context to
non-sighted user.\n\n**Changes made:**\n1. added 'aria-labelledby'
attribute\n\n**Screen:**\n<img width=\"1323\"
alt=\"image\"\nsrc=\"https://github.com/user-attachments/assets/63ffdcca-2139-4302-9dce-ded3a4d3b9a2\"\n/>","sha":"78bf949dbf12a8da845f1fa0e45336eac003eaad","branchLabelMapping":{"^v9.1.0$":"main","^v(\\d+).(\\d+).\\d+$":"$1.$2"}},"sourcePullRequest":{"labels":["Project:Accessibility","release_note:skip","backport:prev-major","v9.1.0"],"title":"fix:
[Platform:StackManagement:Kibana:Spaces] Assign roles to a space flyout
announced
incorrectly","number":218576,"url":"https://github.com/elastic/kibana/pull/218576","mergeCommit":{"message":"fix:
[Platform:StackManagement:Kibana:Spaces] Assign roles to a space flyout
announced incorrectly (#218576)\n\nCloses:
#218351\n\n**Description**\nWhen user clicks on assign new roles to a
space button, the resulting\nflyout gets announced incorrectly as \"you
are in a modal dialog...\"\nwhich doesn't give any context to
non-sighted user.\n\n**Changes made:**\n1. added 'aria-labelledby'
attribute\n\n**Screen:**\n<img width=\"1323\"
alt=\"image\"\nsrc=\"https://github.com/user-attachments/assets/63ffdcca-2139-4302-9dce-ded3a4d3b9a2\"\n/>","sha":"78bf949dbf12a8da845f1fa0e45336eac003eaad"}},"sourceBranch":"main","suggestedTargetBranches":[],"targetPullRequestStates":[{"branch":"main","label":"v9.1.0","branchLabelMappingKey":"^v9.1.0$","isSourceBranch":true,"state":"MERGED","url":"https://github.com/elastic/kibana/pull/218576","number":218576,"mergeCommit":{"message":"fix:
[Platform:StackManagement:Kibana:Spaces] Assign roles to a space flyout
announced incorrectly (#218576)\n\nCloses:
#218351\n\n**Description**\nWhen user clicks on assign new roles to a
space button, the resulting\nflyout gets announced incorrectly as \"you
are in a modal dialog...\"\nwhich doesn't give any context to
non-sighted user.\n\n**Changes made:**\n1. added 'aria-labelledby'
attribute\n\n**Screen:**\n<img width=\"1323\"
alt=\"image\"\nsrc=\"https://github.com/user-attachments/assets/63ffdcca-2139-4302-9dce-ded3a4d3b9a2\"\n/>","sha":"78bf949dbf12a8da845f1fa0e45336eac003eaad"}}]}]
BACKPORT-->

Co-authored-by: Alexey Antonov <alexwizp@gmail.com>

x-pack/platform/plugins/shared/spaces/public/management/edit_space/edit_space_roles_tab.tsx

@@ -106,6 +106,7 @@ export const EditSpaceAssignedRolesTab: FC<Props> = ({ space, features, isReadOn
           size: 'm',
           maxWidth: true,
           maskProps: { headerZindexLocation: 'below' },
+          'aria-labelledby': 'space-assign-role-privilege-form-title',
         }
       );
     },

x-pack/platform/plugins/shared/spaces/public/management/edit_space/roles/component/space_assign_role_privilege_form.tsx

@@ -663,7 +663,7 @@ export const PrivilegesRolesForm: FC<PrivilegesRolesFormProps> = (props) => {
     <React.Fragment>
       <EuiFlyoutHeader hasBorder>
         <EuiTitle size="m">
-          <h2>
+          <h2 id="space-assign-role-privilege-form-title">
             {isEditOperation.current
               ? i18n.translate('xpack.spaces.management.spaceDetails.roles.assignRoleButton', {
                   defaultMessage: 'Edit role privileges for space',