Fix Fedora system test (#5034)

Seems like the latest
[`fedora:41`](https://hub.docker.com/layers/library/fedora/rawhide/images/sha256-c037a87094660ceda037ee319b17f59559241d2a3580d1d0f414e72b0a8f3827?context=explore)
(pushed at Jul 12, 2024 at 22:05 UTC) docker image has removed the
`python3` package, causing our current [CI
failure](https://github.com/astral-sh/uv/actions/runs/9917708846/job/27401528178).

.github/workflows/ci.yml

@@ -637,7 +637,7 @@ jobs:
  - uses: actions/checkout@v4
 
  - name: "Install Python"
- run: dnf install which -y && python3 -m ensurepip
+ run: dnf install python3 which -y && python3 -m ensurepip
 
  - name: "Download binary"
  uses: actions/download-artifact@v4