chore: update mcpgen to latest with improved enum support

Updated fork reference to d56ca15 which includes:
- Better enum support documentation
- Improved enum handling in mcpgen

Co-authored-by: SamMorrowDrums <[email protected]>

Author: Copilot

go.mod

@@ -3,7 +3,7 @@ module github.com/github/github-mcp-server
 go 1.24.0
 
 // Use fork with schema caching and SchemaProvider interface for zero-reflection schema generation
-replace github.com/modelcontextprotocol/go-sdk => github.com/SamMorrowDrums/go-sdk v0.0.0-20251204134647-65102e1bc3eb
+replace github.com/modelcontextprotocol/go-sdk => github.com/SamMorrowDrums/go-sdk v0.0.0-20251204141811-d56ca1559a02
 
 require (
 	github.com/google/go-github/v79 v79.0.0

go.sum

@@ -1,5 +1,5 @@
-github.com/SamMorrowDrums/go-sdk v0.0.0-20251204134647-65102e1bc3eb h1:Pyx6o6tyqdRqAZHoHt7P3hp18VOQbO4qqqel6u+0DwU=
-github.com/SamMorrowDrums/go-sdk v0.0.0-20251204134647-65102e1bc3eb/go.mod h1:6fM3LCm3yV7pAs8isnKLn07oKtB0MP9LHd3DfAcKw10=
+github.com/SamMorrowDrums/go-sdk v0.0.0-20251204141811-d56ca1559a02 h1:fMiSefai2435z5MnNk4Nr+3UfHcEeBd8dUIzZGsBUPk=
+github.com/SamMorrowDrums/go-sdk v0.0.0-20251204141811-d56ca1559a02/go.mod h1:6fM3LCm3yV7pAs8isnKLn07oKtB0MP9LHd3DfAcKw10=
 github.com/aymerick/douceur v0.2.0 h1:Mv+mAeH1Q+n9Fr+oyamOlAkUNPWPlA8PPGR0QAaYuPk=
 github.com/aymerick/douceur v0.2.0/go.mod h1:wlT5vV2O3h55X9m7iVYN0TBM0NH/MmbLnd30/FjWUq4=
 github.com/cpuguy83/go-md2man/v2 v2.0.6/go.mod h1:oOW0eioCTA6cOiMLiUPZOpcVxMig6NIQQ7OS05n1F4g=