ci: Cache Windows boost install #2053

Job	Run time
build-test-server-windows-curl	26m 33s
contract-tests-fdv2	5m 20s
contract-tests	5m 24s
contract-tests-fdv2-curl	5m 21s
contract-tests-curl	5m 2s
build-test-server	8m 57s
build-test-server-mac-curl	5m 19s
build-test-server-curl	9m 29s
build-test-server-mac	4m 48s
build-test-server-windows	22m 38s
	1h 38m 51s

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