Add missing license headers to workflow files

Signed-off-by: Holger Frydrych <holger.frydrych@tngtech.com>

Author: fholger

.github/workflows/check_codestyle.yml

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: 2023 spdx contributors
+#
+# SPDX-License-Identifier: Apache-2.0
+
 name: Run Linter
 
 on:

.github/workflows/install_and_test.yml

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: 2023 spdx contributors
+#
+# SPDX-License-Identifier: Apache-2.0
+
 name: Install and Test
 
 on:

.github/workflows/prepare_release.yml

@@ -1,3 +1,7 @@
+# SPDX-FileCopyrightText: 2023 spdx contributors
+#
+# SPDX-License-Identifier: Apache-2.0
+
 name: Prepare release
 
 on: