[license] use CC0-1.0 for config files

.gitignore

+# SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder
+# SPDX-License-Identifier: CC0-1.0
+
 # build system clutter
 build-*
 Testing

.mailmap

+# SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder
+# SPDX-License-Identifier: CC0-1.0
+
 # This file maps users that have used several mail adresses and user names
 # throughout their contribution history to a unique name-email pair.
 #

.pylintrc

+# SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder
+# SPDX-License-Identifier: CC0-1.0
+
 [MAIN]
 
 # A comma-separated list of package or module names from where C extensions may

bin/.gitignore

+# SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder
+# SPDX-License-Identifier: CC0-1.0
+
 *.pyc

cmake.opts

+# SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder
+# SPDX-License-Identifier: CC0-1.0
+
 GXX_RELEASE_WARNING_OPTS=" \
     -Wall \
     -Wunused \

codemeta.json.license

+SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder
+SPDX-License-Identifier: CC0-1.0

doc/handbook/.gitignore

+# SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder
+# SPDX-License-Identifier: CC0-1.0
+
 #Ignore jabref backup files
 *.bak

docker.opts

+# SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder
+# SPDX-License-Identifier: CC0-1.0
+
 GXX_RELEASE_WARNING_OPTS=" \
     -Wall \
     -Wunused \

pyproject.toml.license

+# SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder
+# SPDX-License-Identifier: CC0-1.0

requirements.txt

+# SPDX-FileCopyrightInfo: Copyright © DuMux Project contributors, see AUTHORS.md in root folder
+# SPDX-License-Identifier: CC0-1.0
+
 numpy
 matplotlib
 pylint~=2.14.0