Update CHANGELOG-EE.md for 12.9.4-ee

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CHANGELOG-EE.md

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+## 12.9.4 (2020-04-16)
+
+### Fixed (2 changes)
+
+- Update index_options to fix advanced search queries. !28712
+- Geo: Fix repository verification on the primary. !28893
+
+### Other (1 change)
+
+- Use prefix search instead of ngrams for sha fields. !27597
+
+
 ## 12.9.3 (2020-04-14)
 
 ### Security (1 change)

ee/changelogs/unreleased/213265-fix-search-for-complex-queries.yml

----
-title: Update index_options to fix advanced search queries
-merge_request: 28712
-author:
-type: fixed

ee/changelogs/unreleased/27789-sha-prefix-search.yml

----
-title: Use prefix search instead of ngrams for sha fields
-merge_request: 27597
-author:
-type: other

ee/changelogs/unreleased/mk-fix-primary-verification.yml

----
-title: 'Geo: Fix repository verification on the primary'
-merge_request: 28893
-author:
-type: fixed