[release/10.0.1xx-preview1] Make this the .NET 10 P1 release branch.

Author: rolfbjarne

Make.config

@@ -141,7 +141,7 @@ endif
 ## Note that the prerelease identifier should be as short as possible, because otherwise
 ## the resulting package name can become too long for MSIs.
 NUGET_HARDCODED_PRERELEASE_IDENTIFIER=net10-p1
-NUGET_HARDCODED_PRERELEASE_BRANCH=net10.0
+NUGET_HARDCODED_PRERELEASE_BRANCH=release/10.0.1xx-preview1
 
 # compute the alphanumeric version of branch names
 NUGET_RELEASE_BRANCH_ALPHANUMERIC:=$(shell export LANG=C; printf "%s" "$(NUGET_RELEASE_BRANCH)" | tr -c '[a-zA-Z0-9-]' '-')