[cross-project-tests] Update code to use mlir::cast (NFC)

/llvm-project/cross-project-tests/debuginfo-tests/llvm-prettyprinters/gdb/mlir-support.cpp:41:16:
 error: 'cast' is deprecated: Use mlir::cast<U>() instead [-Werror,-Wdeprecated-declarations]
    VectorType.cast<mlir::ShapedType>(), llvm::ArrayRef<float>{2.0f, 3.0f});
               ^
/llvm-project/llvm/../mlir/include/mlir/IR/Types.h:345:9: note: 'cast' has been explicitly marked deprecated here
U Type::cast() const {
        ^
/llvm-project/cross-project-tests/debuginfo-tests/llvm-prettyprinters/gdb/mlir-support.cpp:41:16:
 error: 'cast<mlir::ShapedType>' is deprecated: Use mlir::cast<U>() instead [-Werror,-Wdeprecated-declarations]
    VectorType.cast<mlir::ShapedType>(), llvm::ArrayRef<float>{2.0f, 3.0f});
               ^
/llvm-project/llvm/../mlir/include/mlir/IR/Types.h:112:5: note: 'cast<mlir::ShapedType>' has been explicitly marked deprecated here
  [[deprecated("Use mlir::cast<U>() instead")]]
    ^
2 errors generated.

cross-project-tests/debuginfo-tests/llvm-prettyprinters/gdb/mlir-support.cpp

@@ -38,7 +38,7 @@ mlir::Attribute TypeAttr = mlir::TypeAttr::get(IndexType);
 mlir::Attribute ArrayAttr = mlir::ArrayAttr::get(&Context, {UnitAttr});
 mlir::Attribute StringAttr = mlir::StringAttr::get(&Context, "foo");
 mlir::Attribute ElementsAttr = mlir::DenseElementsAttr::get(
-    VectorType.cast<mlir::ShapedType>(), llvm::ArrayRef<float>{2.0f, 3.0f});
+    mlir::cast<mlir::ShapedType>(VectorType), llvm::ArrayRef<float>{2.0f, 3.0f});
 
 int main() {
   // Reference symbols that might otherwise be stripped.