[no ci] bump nightly version

ringo-but-quantum · austingmhuang · commit 8262b054c998 · 2025-05-06T11:37:34.000-04:00
diff --git a/pennylane/_version.py b/pennylane/_version.py
@@ -16,4 +16,4 @@
 Version number (major.minor.patch[-label])
 """
 
-__version__ = "0.42.0-dev19"
+__version__ = "0.42.0-dev20"
