Update nb-tester to 2.1 release candidate

Author: kaelynj

scripts/nb-tester/requirements.txt

@@ -1,7 +1,7 @@
 # We pin to exact versions for a more reproducible and
 # stable build.
 
-qiskit[all]~=2.0.0
+qiskit[all]~=2.1.0rc1
 qiskit-ibm-runtime~=0.37.0
 qiskit-ibm-transpiler[ai-local-mode]~=0.11.0
 qiskit-aer~=0.17