Upgrade pip via upgrade_deps=True

Author: hugovk

build_docs.py

@@ -821,9 +821,14 @@ def build_venv(self) -> None:
             # build, which may recreate it mid-build.
             venv_name += f"-{self.select_output}"
         venv_path = self.build_root / venv_name
-        venv.create(venv_path, symlinks=os.name != "nt", with_pip=True, clear=True)
+        venv.create(
+            venv_path,
+            symlinks=os.name != "nt",
+            with_pip=True,
+            clear=True,
+            upgrade_deps=True,
+        )
         python = venv_path / "bin" / "python"
-        run((python, "-m", "pip", "install", "--upgrade", "pip"))
 
         if (self.checkout / "Doc" / "pylock.toml").exists():
             requirements.remove("-rrequirements.txt")