sip: patch: support absolute filepath in name argument

[Milan Hauth]

sip-6.6.1/sipbuild/distinfo/distinfo.py

```diff
-    real_distinfo_dir = prefix_dir + distinfo_dir
+    real_distinfo_dir = os.path.join(prefix_dir, distinfo_dir)
```

example input, as generated by pyqt-builder:

prefix_dir = /build/tmp0ou30mo2
distinfo_dir = /build/tmp0ou30mo2/wheel/PyQt6-6.3.0.dist-info

actual: /build/tmp0ou30mo2/build/tmp0ou30mo2/wheel/PyQt6-6.3.0.dist-info
expected: /build/tmp0ou30mo2/wheel/PyQt6-6.3.0.dist-info

test:
os.path.join(
  "/build/tmp0ou30mo2",
  "/build/tmp0ou30mo2/wheel/PyQt6-6.3.0.dist-info"
)