Update dependency serverless to v3.38.0 #2273

Job	Run time
Dependencies, Unit tests (16)	1m 31s
Static analysis	6m 33s
Dependencies, Unit tests (18)	1m 30s
Dependencies, Unit tests (20)	1m 27s
Build libraries	4m 5s
Build application (govuk-docs)	2m 35s
Build application (govuk-template)	1m 43s
Test application (govuk-docs, chromium)	1m 26s
Test application (govuk-docs, firefox)	1m 21s
Test application (govuk-docs, electron)	1m 36s
Test application (govuk-template, chromium)	2m 3s
Test application (govuk-template, firefox)	1m 46s
Test application (govuk-template, electron)	1m 16s
	28m 52s

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