Replace hardcoded config fallback version with dynamic constant

Previously, when loading the config file, the fallback version `”0.3.0"` was hardcoded
to handle unversioned configs from earlier releases.

This commit replaces the hardcoded value with the centralized `version` constant,
ensuring consistency across the codebase and reducing the risk of version mismatches
in the future.

Author: belkhadir

Sources/Swiftly/Config.swift

@@ -32,7 +32,7 @@ public struct Config: Codable, Equatable, Sendable {
             if config.version == nil {
                 // Assume that the version of swiftly is 0.3.0 because that is the last
                 // unversioned release.
-                config.version = try? SwiftlyVersion(parsing: "0.3.0")
+                config.version = SwiftlyCore.version
             }
             return config
         } catch {