Fix indentation in Product.swift (#7427)

### Modifications:
Fix indentation in `Product.swift`

### Result:
- [x] I executed SwiftFormat and checked that the indentation remained
corrected.

Sources/PackageDescription/Product.swift

@@ -69,7 +69,6 @@ public class Product {
 
  /// The executable product of a Swift package.
  public final class Executable: Product {
-
  /// The names of the targets in this product.
  public let targets: [String]
 
@@ -149,7 +148,7 @@ public class Product {
  /// - name: The name of the executable product.
  /// - targets: The targets to bundle into an executable product.
  /// - Returns: A `Product` instance.
-public static func executable(
+ public static func executable(
  name: String,
  targets: [String]
  ) -> Product {
@@ -167,7 +166,7 @@ public static func executable(
  /// - name: The name of the plugin product.
  /// - targets: The plugin targets to vend as a product.
  /// - Returns: A `Product` instance.
-@available(_PackageDescription, introduced: 5.5)
+ @available(_PackageDescription, introduced: 5.5)
  public static func plugin(
  name: String,
  targets: [String]