Flaky test: TestBasicGhaCacheImportExport

[crazy-max]

https://github.com/moby/buildkit/actions/runs/11720913396/job/32647699951?pr=5492#step:8:1761

 === FAIL: client TestIntegration/TestBasicGhaCacheImportExport/worker=containerd (601.46s)
    client_test.go:5615: 
        	Error Trace:	/src/client/client_test.go:5615
        	            				/src/client/client_test.go:6004
        	            				/src/util/testutil/integration/run.go:97
        	            				/src/util/testutil/integration/run.go:211
        	Error:      	Received unexpected error:
        	            	maximum timeout reached
        	            	github.com/moby/buildkit/util/stack.Enable
        	            		/src/util/stack/stack.go:82
        	            	github.com/moby/buildkit/util/grpcerrors.FromGRPC
        	            		/src/util/grpcerrors/grpcerrors.go:204
        	            	github.com/moby/buildkit/util/grpcerrors.UnaryClientInterceptor
        	            		/src/util/grpcerrors/intercept.go:41
        	            	google.golang.org/grpc.(*ClientConn).Invoke
        	            		/src/vendor/google.golang.org/grpc/call.go:35
        	            	github.com/moby/buildkit/api/services/control.(*controlClient).Solve
        	            		/src/api/services/control/control_grpc.pb.go:88
        	            	github.com/moby/buildkit/client.(*Client).solve.func2
        	            		/src/client/solve.go:269
        	            	golang.org/x/sync/errgroup.(*Group).Go.func1
        	            		/src/vendor/golang.org/x/sync/errgroup/errgroup.go:78
        	            	runtime.goexit
        	            		/usr/local/go/src/runtime/asm_amd64.s:1700
        	            	failed to solve
        	            	github.com/moby/buildkit/client.(*Client).solve.func2
        	            		/src/client/solve.go:285
        	            	golang.org/x/sync/errgroup.(*Group).Go.func1
        	            		/src/vendor/golang.org/x/sync/errgroup/errgroup.go:78
        	            	runtime.goexit
        	            		/usr/local/go/src/runtime/asm_amd64.s:1700

We encounter this one when a bunch of jobs are running on CI and therefore we got rate-limited in GHA cache backend with this test.

Also happens on moby repo when running buildkit integration tests: #3694 (comment) (cc @thaJeztah @vvoland)

We could increase timeout in this test to mitigate this issue.