Update setup-uv docs for Github Actions integration guide (re-order python and uv setup) (#14741)

I updated the Github Actions integration guide to run Github's
`setup-python` before Astral's `setup-uv`, as `setup-uv`'s
`activate-environment: true` doesn't work with the original ordering.
There is a discussion about this behavior in the `setup-uv` repo
[here](astral-sh/setup-uv#479).

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## Summary

Update the documentation for the Github Actions integration. Caveat: I'm
unsure if there are any other reasons where the original ordering (that
is,`setup-uv` before `setup-python`) might be preferred.

## Test Plan

Tested in a private Github Actions push, as documented in the
aforementioned discussion on `setup-uv`'s repo. Confirmed that removing
`source .venv/bin/activate` and replacing it with `activate-environment:
true` now works in this ordering (but didn't work with the original
ordering where `uv` installs before Github's `python`).

Author: alichaudry

docs/guides/integration/github.md

@@ -92,13 +92,13 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Install uv
-        uses: astral-sh/setup-uv@v6
-
       - name: "Set up Python"
         uses: actions/setup-python@v5
         with:
           python-version-file: ".python-version"
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v6
 ```
 
 Or, specify the `pyproject.toml` file to ignore the pin and use the latest version compatible with
@@ -115,13 +115,13 @@ jobs:
     steps:
       - uses: actions/checkout@v4
 
-      - name: Install uv
-        uses: astral-sh/setup-uv@v6
-
       - name: "Set up Python"
         uses: actions/setup-python@v5
         with:
           python-version-file: "pyproject.toml"
+
+      - name: Install uv
+        uses: astral-sh/setup-uv@v6
 ```
 
 ## Multiple Python versions