fix(build): fix Python warning

f"\S" is interpreted as f"\\S", but a warning is issued by Python:

    tools/collect-copyright:837: SyntaxWarning: invalid escape sequence '\S'
      match = re.match(f"^(?P<package>\S+): (?P<file>.*)$", line)

Fix this warning by writing f"\\S" explicitly.

tools/collect-copyright

@@ -834,7 +834,7 @@ class Debian:
 
         packages = []
         for line in process.stdout.splitlines():
-            match = re.match(f"^(?P<package>\S+): (?P<file>.*)$", line)
+            match = re.match(f"^(?P<package>\\S+): (?P<file>.*)$", line)
             if match is not None:
                 file = match.group("file")
                 package_name = match.group("package")