Bump software.amazon.awssdk:bom from 2.20.12 to 2.21.5 in /backend #5386

Job	Run time
analyze-backend	0s
audit-licenses-frontend	37s
audit-licenses-backend	3m 32s
analyze-frontend	0s
backend-build	2m 26s
backend-build-image-and-scan	3m 40s
backend-integration-tests	5m 42s
backend-unit-tests	4m 35s
deployment-time-check	1m 41s
frontend-build-image-and-scan	1m 11s
frontend-style	1m 27s
frontend-tests	3m 52s
generate-backend-code-documentation	7m 58s
generate-entity-relationship-diagram	0s
prep-playwright-tests	0s
push-frontend-image-to-registry	0s
push-backend-image-to-registry	0s
deploy-staging	0s
e2e-tests	0s
check-latest-deploy-tag	0s
deploy-production	0s
deploy-uat	0s
push-reports	0s
	36m 41s

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