Ignore auto-generated .substvars files

Signed-off-by: Lars Froehlich <lars.froehlich@desy.de>

Author: alt-graph

.gitignore

@@ -4,3 +4,4 @@ docs/html/
 .vscode/settings.json
 .vscode/cspell.json
 unit_test_files/
+debian/libgit4cpp-*.substvars