Add type annotation for get_lines

pytensor/link/c/cmodule.py

@@ -2104,7 +2104,7 @@ class GCC_compiler(Compiler):
             )
             detect_march = False
 
-        def get_lines(cmd, parse=True):
+        def get_lines(cmd: list[str] | str, parse: bool = True) -> list[str] | None:
             p = subprocess_Popen(
                 cmd,
                 stdout=subprocess.PIPE,