[3.12] gh-117535: Ignore makeup file name "sys" for warnings

[gaogaotiantian]

"sys" is a makeup filename in

    except ValueError:
        globals = sys.__dict__
        filename = "sys"
        lineno = 1

so we should never try to get the source code for it. Otherwise if there happens to be a sys file in sys.path, the first line will be displayed.

This is a backward compatible patch for backport only. We will have some new solution for main

• Issue: RuntimeWarning "coroutine was never awaited" prints first line of file called sys #117535

[serhiy-storchaka]

LGTM.