[net8.0] Bump ro rc1 since we just branched

Make.config

@@ -125,7 +125,7 @@ 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=net8-p7
+NUGET_HARDCODED_PRERELEASE_IDENTIFIER=net8-rc1
 NUGET_HARDCODED_PRERELEASE_BRANCH=net8.0
 
 # compute the alphanumeric version of branch names