Fixed the following compiler errors and warning.

* QuickTaskInfoEditForm.cs(57, 124): [CS8107] Feature 'enum generic type constraints' is not available in C# 7.0. Please use language version 7.3 or greater.

* VideoConverterForm.cs(177, 25): [CS0121] The call is ambiguous between the following methods or properties: 'Task.Run<TResult>(Func<TResult>)' and 'Task.Run(Func<Task>)'

* HashCheck.cs(65, 55): [CS0168] The variable 'e' is declared but never used

ShareX.HelpersLib/Cryptographic/HashCheck.cs

@@ -62,7 +62,7 @@ public async Task<string> Start(string filePath, HashType hashType)
                     {
                         return HashCheckThread(filePath, hashType, progress, cts.Token);
                     }
-                    catch (OperationCanceledException e)
+                    catch (OperationCanceledException)
                     {
                     }
 

ShareX.MediaLib/Forms/VideoConverterForm.cs

@@ -174,7 +174,7 @@ private bool StartEncoding()
 
         private Task<bool> StartEncodingAsync()
         {
-            return Task.Run(StartEncoding);
+            return Task.Run(() => StartEncoding());
         }
 
         private void Manager_EncodeProgressChanged(float percentage)

ShareX/ShareX.csproj

@@ -34,6 +34,7 @@
     <UseApplicationTrust>false</UseApplicationTrust>
     <BootstrapperEnabled>true</BootstrapperEnabled>
     <AutoGenerateBindingRedirects>true</AutoGenerateBindingRedirects>
+    <LangVersion>7.3</LangVersion>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)|$(Platform)' == 'Debug|AnyCPU' ">
     <DebugSymbols>true</DebugSymbols>