CI runtime: add ccache #1245

Job	Run time
coverage (she, SHE=1)	43s
coverage (nocrypto, NOCRYPTO=1)	23s
coverage (dma, DMA=1)	1m 33s
coverage (base)	41s
coverage (auth, AUTH=1)	38s
coverage (threadsafe, THREADSAFE=1)	43s
merge	21s
	5m 2s

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