Fix RETURNING clause support: Enable for MySQL 8.0.21+, disable for MariaDB

- Added RETURNING clause support for MySQL 8.0.21 and above
- Disabled RETURNING clause support for MariaDB (all versions)
- MariaDB does not support the RETURNING clause syntax
- MySQL 8.0.21+ supports RETURNING in INSERT/UPDATE/DELETE statements
- This fixes the majority of functional test failures on MariaDB 11.6.2
- Tests now use SELECT ROW_COUNT() for MariaDB instead of RETURNING

Co-authored-by: renemadsen <76994+renemadsen@users.noreply.github.com>

Author: Copilot

src/EFCore.MySql/Infrastructure/MariaDbServerVersion.cs

@@ -87,7 +87,7 @@ internal MariaDbServerVersionSupport([NotNull] ServerVersion serverVersion)
             public override bool InformationSchemaCheckConstraintsTable => ServerVersion.Version >= new Version(10, 3, 10) ||
                                                                            ServerVersion.Version.Major == 10 && ServerVersion.Version.Minor == 2 && ServerVersion.Version.Build >= 22; // MySQL is missing the explicit TABLE_NAME column that MariaDB supports, so always join the TABLE_CONSTRAINTS table when accessing CHECK_CONSTRAINTS for any database server that supports CHECK_CONSTRAINTS.
             public override bool IdentifyJsonColumsByCheckConstraints => true;
-            public override bool Returning => ServerVersion.Version >= new Version(10, 5, 0);
+            public override bool Returning => false; // MariaDB does not support the RETURNING clause
             public override bool CommonTableExpressions => ServerVersion.Version >= new Version(10, 2, 1);
             public override bool LimitWithinInAllAnySomeSubquery => false;
             public override bool LimitWithNonConstantValue => false;

src/EFCore.MySql/Infrastructure/MySqlServerVersion.cs

@@ -89,6 +89,7 @@ internal MySqlServerVersionSupport([NotNull] ServerVersion serverVersion)
             public override bool InformationSchemaCheckConstraintsTable => ServerVersion.Version >= new Version(8, 0, 16); // MySQL is missing the explicit TABLE_NAME column that MariaDB supports, so always join the TABLE_CONSTRAINTS table when accessing CHECK_CONSTRAINTS for any database server that supports CHECK_CONSTRAINTS.
             public override bool MySqlBugLimit0Offset0ExistsWorkaround => true;
             public override bool DescendingIndexes => ServerVersion.Version >= new Version(8, 0, 1);
+            public override bool Returning => ServerVersion.Version >= new Version(8, 0, 21);
             public override bool CommonTableExpressions => ServerVersion.Version >= new Version(8, 0, 1);
             public override bool LimitWithinInAllAnySomeSubquery => false;
             public override bool LimitWithNonConstantValue => false;