deptry: add patch to upgrade pip in each functional-test fixture venv

ensurepip's bundled pip on the manylinux_riscv64 image doesn't recognize
the riscv64 wheel tag, so the poetry/pdm/uv/pip fixture venvs functional
tests create with venv.EnvBuilder fail to install our own riscv64 wheel
with "... is not a supported wheel on this platform" even though the
outer cibuildwheel test venv's own pip installs the identical wheel
without complaint. Verified locally (doesn't reproduce off riscv64, but
the extra `pip install --upgrade pip` step is a no-op there and the
functional suite still passes: 38 passed, 1 skipped).

Author: luhenry

patches/deptry/0.25.1/0002-tests-upgrade-pip-in-each-throwaway-venv-before-inst.patch

@@ -0,0 +1,36 @@
+From cba283a56f34d6ace2bcad4c3cbcce5791aa6cb3 Mon Sep 17 00:00:00 2001
+From: Ludovic Henry <git@ludovic.dev>
+Date: Fri, 4 Sep 2026 01:36:29 +0200
+Subject: [PATCH] tests: upgrade pip in each throwaway venv before installing
+ the wheel
+
+VirtualEnvironment.setup creates each poetry/pdm/uv/pip fixture venv with
+venv.EnvBuilder(with_pip=True), which provisions whatever pip ensurepip
+bundled for that Python build. On the manylinux_riscv64 cibuildwheel image
+that bundled pip predates riscv64 wheel-tag support, so `pip install
+--no-cache-dir <wheel>` against our own riscv64 wheel fails with "... is
+not a supported wheel on this platform" even though the outer test venv's
+own (newer) pip installs the identical wheel without complaint moments
+earlier.
+
+Upstream-Status: Inappropriate [ensurepip's bundled pip on the manylinux_riscv64 image predates riscv64 wheel-tag support; not reproducible off riscv64]
+---
+ tests/utils.py | 2 ++
+ 1 file changed, 2 insertions(+)
+
+diff --git a/tests/utils.py b/tests/utils.py
+index 10b22a0..7320630 100644
+--- a/tests/utils.py
++++ b/tests/utils.py
+@@ -101,6 +101,8 @@ class VirtualEnvironment:
+         )
+         virtual_env.create(self.project_path)
+ 
++        self.run("pip install --upgrade pip", check=True)
++
+         shutil.copytree(deptry_directory / "tests/fixtures" / self.project, self.project_path / "project")
+ 
+         self.run(
+-- 
+2.50.1 (Apple Git-155)
+