Bump trillian-opensource-ci/db_server from `128cd27` to `5420875` in /config/trillian/mysql #1407

Job	Run time
e2e tests for fulcio key rotation (v1.27.x, fulcio-key-rotation, 1.23.x)	8m 40s
e2e tests for fulcio key rotation (v1.28.x, fulcio-key-rotation, 1.23.x)	9m 3s
e2e tests for fulcio key rotation (v1.29.x, fulcio-key-rotation, 1.23.x)	9m 17s
e2e tests for fulcio key rotation (v1.30.x, fulcio-key-rotation, 1.23.x)	9m 2s
	36m 2s

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