Use thread-safe log writer for seeding.

Author: sharpjs

PSql.Deploy.Engine/Seeds/ISeedConsole.cs

@@ -67,6 +67,9 @@ void ReportApplied(ISeedApplication info,
     /// <returns>
     ///   A writer that writes to the log file.
     /// </returns>
+    /// <remarks>
+    ///   Implementations must ensure that the returned writer is thread-safe.
+    /// </remarks>
     /// <exception cref="ArgumentNullException">
     ///   <paramref name="info"/> is <see langword="null"/>.
     /// </exception>

PSql.Deploy/Seeds/CmdletSeedConsole.cs

@@ -49,7 +49,9 @@ public TextWriter CreateLog(S.ISeedApplication info)
 
         var fileName = $"{target}.{seed}.log".SanitizeFileName();
 
-        return new StreamWriter(Path.Combine(_logPath, fileName));
+        return TextWriter.Synchronized(
+            new StreamWriter(Path.Combine(_logPath, fileName))
+        );
     }
 
     /// <inheritdoc/>