Flaky test in zpages span processor

[dmathieu]

Description

We have a flaky test in the zpages module's span processor tests.

--- FAIL: TestSpanProcessorFuzzer (0.06s)
    spanprocessor_test.go:111: 
        	Error Trace:	D:/a/opentelemetry-go-contrib/opentelemetry-go-contrib/zpages/spanprocessor_test.go:111
        	Error:      	"0" is not greater than or equal to "1"
        	Test:       	TestSpanProcessorFuzzer

See https://github.com/open-telemetry/opentelemetry-go-contrib/actions/runs/17317518500/job/49163181772

[dmathieu]

cc @dashpole as code owner.

[tdn21]

Please assign this issue to me, i'll take a look. Thank you! 🙇