Reverted temporary Solr dependency on CI #1403

Job	Run time
Run code style check (8.0)	2m 41s
Unit tests & SQLite integration tests (7.4)	6m 56s
Solr integration tests (7.4)	9m 36s
Unit tests & SQLite integration tests (8.0)	6m 58s
Solr integration tests (8.0)	9m 54s
Unit tests & SQLite integration tests (8.1)	7m 1s
Solr integration tests (8.1)	9m 40s
MySQL integration tests (7.4)	12m 55s
MySQL integration tests (8.0)	12m 39s
PostgreSQL integration tests (7.4)	28m 38s
MySQL integration tests (8.1)	12m 48s
PostgreSQL integration tests (8.0)	29m 28s
PostgreSQL integration tests (8.1)	23m 46s
	2h 53m 0s

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