automation: Update matrix-synapse Docker tag to v1.74.0

This MR contains the following updates:

Package	Update	Change
matrix-synapse	minor	1.73.0 -> 1.74.0

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Release Notes

matrix-org/synapse

v1.74.0

Compare Source

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Improved Documentation

• Add release note and update documentation regarding optional ICU support in user search. (#​14712)

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