fix: not setting field boost

Author: hazzik

src/NHibernate.Search.Tests/FieldAccess/FieldAccessTest.cs

@@ -10,6 +10,8 @@ namespace NHibernate.Search.Tests.FieldAccess
     [TestFixture]
     public class FieldAccessTest : SearchTestCase
     {
+        protected override bool RunFixtureSetUpAndTearDownForEachTest => true;
+
         protected override IList Mappings
         {
             get

src/NHibernate.Search/Mapping/AttributeBased/AttributeSearchMappingBuilder.cs

@@ -230,7 +230,8 @@ private void BuildProperty(
                     ) {
                         Store = fieldAttribute.Store,
                         Index = fieldAttribute.Index,
-                        Analyzer = fieldAnalyzer
+                        Analyzer = fieldAnalyzer,
+                        Boost = boost
                     };
 
                     documentMapping.Fields.Add(field);