Switch to REUSE.toml, restrict PR license check to modified files

.github/workflows/checks.yml

@@ -20,7 +20,18 @@ jobs:
     - name: Checkout source code
       uses: actions/checkout@v4
 
-    - name: Validate licenses
+    - name: Validate license (pull request)
+      if: github.event_name == 'pull_request'
+      working-directory: ${{github.workspace}}
+      run: |
+        git diff --name-only ${{ github.event.base_ref }} ${{ github.event.head_ref }} \
+            | sed -E 's/\.license$//' \
+            | sort -u \
+            | xargs -d '\n' ls -1d 2>/dev/null \
+            | xargs -d '\n' python3 -m pipx run reuse lint-files --
+
+    - name: Validate licenses (push)
+      if: github.event_name == 'push'
       working-directory: ${{github.workspace}}
       run: |
         python3 -m pipx run reuse lint

REUSE.toml

@@ -0,0 +1,22 @@
+version = 1
+SPDX-PackageName = "Celestia Content"
+SPDX-PackageSupplier = "Celestia Development Team"
+SPDX-PackageDownloadLocation = "https://github.com/CelestiaProject/CelestiaContent"
+
+[[annotations]]
+path = "README"
+precedence = "aggregate"
+SPDX-FileCopyrightText = "Celestia Development Team"
+SPDX-License-Identifier = "GPL-2.0-or-later"
+
+[[annotations]]
+path = ".github/**"
+precedence = "aggregate"
+SPDX-FileCopyrightText = "Celestia Development Team"
+SPDX-License-Identifier = "GPL-2.0-or-later"
+
+[[annotations]]
+path = "debian/**"
+precedence = "aggregate"
+SPDX-FileCopyrightText = ["2001-2002 Marcelo E. Magallon <[email protected]>", "2003 Mika Fischer <[email protected]>", "2005 Mathias Weyland <[email protected]>", "2007-2013 Guus Sliepen <[email protected]>", "2019 Celestia Development Team"]
+SPDX-License-Identifier = "GPL-2.0-or-later"