Fix errNotImplemented reference

[aknuds1]

Replace notImplementedErr reference with errNotImplemented in prometheus/process_collector_mem_nocgo_darwin.go, since the former doesn't exist any longer. This fixes compilation on Mac.

[Copilot]

Pull Request Overview

Fixes a reference to the correct errNotImplemented variable in the Darwin non-cgo memory collector stub.

• Replace the undefined notImplementedErr with the existing errNotImplemented in getMemory.
• Ensures the stub compiles against the shared error constant.

Comments suppressed due to low confidence (1)

prometheus/process_collector_mem_nocgo_darwin.go:19

• Consider adding a unit test to verify that getMemory on Darwin without cgo returns errNotImplemented as expected, ensuring this stub behavior is covered.

	return nil, errNotImplemented

[kakkoyun]

Thanks for quick action.