Fix intermittent cache test failures

Job #658818771 failed for 43f724fe:

    --- FAIL: TestResolve/when_retrieval_failed_because_of_resolution_context_being_canceled (0.00s)
        cache_test.go:264: 
            	Error Trace:	cache_test.go:264
            	            				cache_test.go:113
            	            				cache_test.go:253
            	            				cache_test.go:93
            	            				cache_test.go:252
            	Error:      	An error is expected but got nil.
            	Test:       	TestResolve/when_retrieval_failed_because_of_resolution_context_being_canceled

Another job https://gitlab.com/gitlab-org/gitlab-pages/-/jobs/658818891

=== RUN   TestResolve/when_item_is_in_long_cache_only
    cache_test.go:207: 
        	Error Trace:	cache_test.go:207
        	            				cache_test.go:113
        	            				cache_test.go:200
        	            				cache_test.go:93
        	            				cache_test.go:199
        	Error:      	Not equal: 
        	            	expected: 0x1
        	            	actual  : 0x0
        	Test:       	TestResolve/when_item_is_in_long_cache_only

Retrying a job fixes it https://gitlab.com/gitlab-org/gitlab-pages/-/jobs/658821575