style(pm): add license to workspace

Without this, there's an issue where josh tries to recreate the license
file in pushes without realizing that it should be alongside the
workspace file...

packetmix/workspace.josh.license

···
+SPDX-FileCopyrightText: 2025 FreshlyBakedCake
+
+SPDX-License-Identifier: CC0-1.0

projects/packetmix/workspace.josh

···
 ::.tangled/
 ::LICENSES/
+::projects/packetmix/workspace.josh.license
 :/packetmix