setuptools-rust: fix build due to missing setup.py.

Looks like PyPi tarball doesn't have setup.py, which jhbuild needs:
*** Checking out python3-setuptools_rust *** [66/137]
*** Building python3-setuptools_rust *** [66/137]
python3 setup.py build --build-base /Users/runner/.cache/jhbuild/build/setuptools-rust-1.8.1
python3: can't open file '/Users/runner/gtk/source/setuptools-rust-1.8.1/setup.py': [Errno 2] No such file or directory
*** Error during phase build of python3-setuptools_rust: ########## Error running python3 setup.py build --build-base /Users/runner/.cache/jhbuild/build/setuptools-rust-1.8.1 *** [66/137]

Add it back using a patch.

Xpra-org/xpra#4017 (comment)

patches/setuptools-rust-setup-py.patch

@@ -0,0 +1,16 @@
+commit 61401d62c557246600b45d09d471450e97b8c6f0
+Author: Catalin Patulea <[email protected]>
+Date:   Sat Jan 27 11:32:52 2024 +0000
+
+    Add skeleton setup.py.
+
+diff --git a/setup.py b/setup.py
+new file mode 100755
+index 0000000..851cb3f
+--- /dev/null
++++ b/setup.py
+@@ -0,0 +1,3 @@
++#!/usr/bin/env python3
++from setuptools import setup
++setup()
+\ No newline at end of file

xpra-python3.modules

@@ -171,7 +171,9 @@
 		<branch
 			module="s/setuptools-rust/setuptools-rust-1.8.1.tar.gz"
 			hash="sha256:94b1dd5d5308b3138d5b933c3a2b55e6d6927d1a22632e509fcea9ddd0f7e486"
-			version="1.8.1"/>
+			version="1.8.1">
+			<patch file="setuptools-rust-setup-py.patch" strip="1"/>
+		</branch>
 		<dependencies>
 			<dep package="python3"/>
 			<dep package="python3-semantic-version"/>