release: bump workspace version to 2.1.1

The About modal reads CARGO_PKG_VERSION, so it showed 2.1.0. Bump the workspace
version (and the Cargo.lock members) to 2.1.1 and add the 2.1.1 metainfo release
entry.

cc

crates/Cargo.toml

@@ -65,7 +65,7 @@ members = [
 default-members = ["qbz-qt"]
 
 [workspace.package]
-version = "2.1.0"
+version = "2.1.1"
 edition = "2021"
 license = "MIT"
 repository = "https://github.com/vicrodh/qbz"