Fix list initializer in bulk Execute README example

[dajiaohuang]

Problem

The existing-collection example in “Execute a Command multiple times” does not compile. Copying its var foos = new List<Foo> { ... }; initializer into a console project, with a Foo class exposing A and B, reports CS1003 at the first two entries. Each entry has an extra pair of initializer braces and the entries lack separating commas.

Change

Use three comma-separated new Foo { ... } elements. No API or runtime changes.

Validation

• Original initializer extracted verbatim from Readme.md: compilation fails with CS1003.
• Corrected initializer: compiles and prints a count of 3 (.NET SDK 10.0.100, net10.0).
• Core Dapper Release/net10.0 build: 0 warnings/errors, invoked outside the checkout because the installed SDK is older than the pinned 10.0.102.
• Standalone in-memory SQLite checks against the built library pass, including bulk Execute using this list (three inserted rows). SQLite-compatible INSERT syntax and exact-case parameter names were used; this is not a SQL Server test.

The database-dependent native test suite was not run. The change is limited to the three README initializer lines.