automation: Update matrix-synapse Docker tag to v1.108.0

This MR contains the following updates:

Package	Update	Change
matrix-synapse (source)	minor	1.106.0 -> 1.108.0

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Release Notes

element-hq/synapse (matrix-synapse)

v1.108.0

Compare Source

No significant changes since 1.108.0rc1.

v1.107.0

Compare Source

============================

No significant changes since 1.107.0rc1.

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