Fix code style warnings in test project when targeting .NET 8

see 69b923ad5

src/BizHawk.Common/Util.cs

@@ -66,11 +66,13 @@ namespace BizHawk.Common
 			return data;
 		}
 
+#if !(NETSTANDARD2_1_OR_GREATER || NETCOREAPP2_0_OR_GREATER)
 		public static void Deconstruct<TKey, TValue>(this KeyValuePair<TKey, TValue> kvp, out TKey key, out TValue value)
 		{
 			key = kvp.Key;
 			value = kvp.Value;
 		}
+#endif
 
 		/// <remarks>adapted from https://stackoverflow.com/a/3928856/7467292, values are compared using <see cref="EqualityComparer{T}.Default">EqualityComparer.Default</see></remarks>
 		public static bool DictionaryEqual<TKey, TValue>(IDictionary<TKey, TValue> a, IDictionary<TKey, TValue> b)

src/BizHawk.Tests/Client.Common/config/CorePickerStabilityTests.cs

@@ -29,7 +29,9 @@ namespace BizHawk.Tests.Client.Common.config
 					appliesTo.All(multiCoreSystems.Contains),
 					appliesTo.Length is 1
 						? $"core picker has submenu for {appliesTo[0]}, but that system doesn't have alternate cores"
+#pragma warning disable MA0089 // CI build this for .NET Core where there's a `char` overload for `string.Join`
 						: $"core picker has submenu for {appliesTo[0]} ({string.Join("/", appliesTo)}), but none of those systems have alternate cores");
+#pragma warning restore MA0089
 			}
 		}
 

src/BizHawk.Tests/Client.Common/config/SerializationStabilityTests.cs

@@ -3,7 +3,9 @@ using System.Drawing;
 using System.Reflection;
 
 using BizHawk.Client.Common;
+#if !(NETSTANDARD2_1_OR_GREATER || NETCOREAPP2_0_OR_GREATER)
 using BizHawk.Common;
+#endif
 
 using Newtonsoft.Json;
 using Newtonsoft.Json.Linq;

src/BizHawk.Tests/Emulation.Common/Database/FirmwareDatabaseTests.cs

@@ -47,9 +47,11 @@ namespace BizHawk.Tests.Emulation.Common
 				}
 			}
 			if (dupes.Count is 0) return;
+#pragma warning disable MA0089 // CI build this for .NET Core where there's a `char` overload for `string.Join`
 			Assert.Fail($"multiple {nameof(FirmwareFile)}s have the same suggested filename (breaks Organize function):\n{
 				string.Join("\n", dupes.Select(static ff => $"\t{ff.RecommendedName} {ff.Hash}").Order())
 			}");
+#pragma warning restore MA0089
 		}
 	}
 }