[8.9] [Cases] Test case_view_activity.test.tsx suite (elastic#160639)…

… (elastic#160930)

# Backport

This will backport the following commits from `main` to `8.9`:
- [[Cases] Test `case_view_activity.test.tsx` suite
(elastic#160639)](elastic#160639)

<!--- Backport version: 8.9.7 -->

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

<!--BACKPORT [{"author":{"name":"Christos
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Test `case_view_activity.test.tsx` suite (elastic#160639)\n\n##
Summary\r\n\r\nFixes flaky tests
in\r\n`x-pack/plugins/cases/public/components/case_view/components/case_view_activity.test.tsx`\r\n\r\nSuccessful
runs:\r\n\r\n-\r\nhttps://github.com/elastic/pull/160639/commits/a7a19c1a74df5ca9202dcb1516b9284d3faf2b2a\r\n(40
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Checklist\r\n\r\nDelete any items that are not applicable to this
PR.\r\n\r\n- [x] [Unit or
functional\r\ntests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)\r\nwere
updated or added to match the most common scenarios\r\n\r\n### For
maintainers\r\n\r\n- [x] This was checked for breaking API changes and
was
[labeled\r\nappropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)\r\n\r\n---------\r\n\r\nCo-authored-by:
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Test `case_view_activity.test.tsx` suite (elastic#160639)\n\n##
Summary\r\n\r\nFixes flaky tests
in\r\n`x-pack/plugins/cases/public/components/case_view/components/case_view_activity.test.tsx`\r\n\r\nSuccessful
runs:\r\n\r\n-\r\nhttps://github.com/elastic/pull/160639/commits/a7a19c1a74df5ca9202dcb1516b9284d3faf2b2a\r\n(40
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https://github.com/elastic/kibana/issues/151981,\r\nhttps://github.com/elastic/kibana/issues/151979,\r\nhttps://github.com/elastic/kibana/issues/151980,\r\nhttps://github.com/elastic/kibana/issues/152209,\r\nhttps://github.com/elastic/kibana/issues/152207,\r\nhttps://github.com/elastic/kibana/issues/152208,\r\nhttps://github.com/elastic/kibana/issues/152203,\r\nhttps://github.com/elastic/kibana/issues/152203,\r\nhttps://github.com/elastic/kibana/issues/152201,\r\nhttps://github.com/elastic/kibana/issues/152206,\r\nhttps://github.com/elastic/kibana/issues/152202,https://github.com/elastic/kibana/issues/152205,\r\nhttps://github.com/elastic/kibana/issues/152204,\r\nhttps://github.com/elastic/kibana/issues/152200\r\n\r\n###
Checklist\r\n\r\nDelete any items that are not applicable to this
PR.\r\n\r\n- [x] [Unit or
functional\r\ntests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)\r\nwere
updated or added to match the most common scenarios\r\n\r\n### For
maintainers\r\n\r\n- [x] This was checked for breaking API changes and
was
[labeled\r\nappropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)\r\n\r\n---------\r\n\r\nCo-authored-by:
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Test `case_view_activity.test.tsx` suite (elastic#160639)\n\n##
Summary\r\n\r\nFixes flaky tests
in\r\n`x-pack/plugins/cases/public/components/case_view/components/case_view_activity.test.tsx`\r\n\r\nSuccessful
runs:\r\n\r\n-\r\nhttps://github.com/elastic/pull/160639/commits/a7a19c1a74df5ca9202dcb1516b9284d3faf2b2a\r\n(40
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https://github.com/elastic/kibana/issues/151981,\r\nhttps://github.com/elastic/kibana/issues/151979,\r\nhttps://github.com/elastic/kibana/issues/151980,\r\nhttps://github.com/elastic/kibana/issues/152209,\r\nhttps://github.com/elastic/kibana/issues/152207,\r\nhttps://github.com/elastic/kibana/issues/152208,\r\nhttps://github.com/elastic/kibana/issues/152203,\r\nhttps://github.com/elastic/kibana/issues/152203,\r\nhttps://github.com/elastic/kibana/issues/152201,\r\nhttps://github.com/elastic/kibana/issues/152206,\r\nhttps://github.com/elastic/kibana/issues/152202,https://github.com/elastic/kibana/issues/152205,\r\nhttps://github.com/elastic/kibana/issues/152204,\r\nhttps://github.com/elastic/kibana/issues/152200\r\n\r\n###
Checklist\r\n\r\nDelete any items that are not applicable to this
PR.\r\n\r\n- [x] [Unit or
functional\r\ntests](https://www.elastic.co/guide/en/kibana/master/development-tests.html)\r\nwere
updated or added to match the most common scenarios\r\n\r\n### For
maintainers\r\n\r\n- [x] This was checked for breaking API changes and
was
[labeled\r\nappropriately](https://www.elastic.co/guide/en/kibana/master/contributing.html#kibana-release-notes-process)\r\n\r\n---------\r\n\r\nCo-authored-by:
Kibana Machine
<42973632+kibanamachine@users.noreply.github.com>","sha":"6349724ff26d23fe927d8cb69fef642d76b396df"}}]}]
BACKPORT-->

Co-authored-by: Christos Nasikas <christos.nasikas@elastic.co>