ci: install flytectl directly instead of the broken setup action

unionai-oss/flytectl-setup-action resolves the latest flytectl from the
first page of flyteorg/flyte releases. That page is now entirely Flyte 2.0
(v2.0.x) tags with no flytectl/ release, so the action crashes with
"Cannot read properties of undefined (reading 'assets')" and reds the
integration jobs on master and every PR. Download the last flytectl
release (v0.9.8) from its asset URL instead.

Signed-off-by: 1fanwang <1fannnw@gmail.com>

Author: 1fanwang

.github/workflows/pythonbuild.yml

@@ -242,7 +242,12 @@ jobs:
           make setup-global-uv
           uv pip freeze
       - name: Install FlyteCTL
-        uses: unionai-oss/flytectl-setup-action@master
+        # unionai-oss/flytectl-setup-action resolves "latest" from the first page of flyteorg/flyte releases, which is
+        # now all Flyte 2.0 (v2.0.x) tags with no flytectl/ release on page 1, so it crashes on `reading 'assets'`.
+        # Install the last flytectl release directly instead.
+        run: |
+          curl -sL "https://github.com/flyteorg/flyte/releases/download/flytectl/v0.9.8/flytectl_Linux_x86_64.tar.gz" | sudo tar -xz -C /usr/local/bin flytectl
+          flytectl version
       - name: Setup Flyte Sandbox
         run: |
           flytectl demo start --disable-agent