Warnings during build/test

[Charles-Gagnon]

There's a number of compiler warnings during build/test. It'd be good to get these fixed now so new warnings are easier to notice.

• UTA001: TestClass attribute defined on non-public class SqlStudio.Tests. UTSqlScriptDom.DataRetentionSqlScriptDomTests
• MSB3884: Could not find rule set file "AllRules.ruleset". [C:\src\SqlScriptDOM\Test\SqlDom\UTSqlScriptDom.csproj::TargetFramework=net462]
• TSql160ParserInternal_final.cs(79827,8): wa rning CS0219: The variable 'vHasColumnList' is assigned but its value is never used [C:\src\SqlScriptDOM\SqlScriptDom\Microsoft.SqlServer.TransactSql .ScriptDom.csproj::TargetFramework=net6.0]

(there may be others, these were just the initial ones I noticed)