[3.11] GH-95899: fix asyncio.Runner to call set_event_loop only once (GH-95900)

[miss-islington]

(cherry picked from commit 914f636)

Co-authored-by: Kumar Aditya 59607654+kumaraditya303@users.noreply.github.com

• Issue: asyncio.Runner+PidfdChildWatcher leaves zombie processes #95899

[miss-islington]

Status check is done, and it's a success ✅ .

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @gvanrossum for commit d500d1a 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[kumaraditya303]

FYI the macOS failure is known to be flaky #95241 and is unrelated.

[gvanrossum]

I'll wait for most of the buildbots to complete and then merge. Thanks all! (Alas, there may be one more coming, see #95898.)

[miss-islington]

@kumaraditya303 and @gvanrossum: Status check is done, and it's a failure ❌ .

[miss-islington]

@kumaraditya303 and @gvanrossum: Status check is done, and it's a failure ❌ .

[miss-islington]

@kumaraditya303 and @gvanrossum: Status check is done, and it's a failure ❌.

[miss-islington]

@kumaraditya303 and @gvanrossum: Status check is done, and it's a failure ❌.

[miss-islington]

@kumaraditya303 and @gvanrossum: Status check is done, and it's a failure ❌.

[miss-islington]

@kumaraditya303 and @gvanrossum: Status check is done, and it's a failure ❌.

[miss-islington]

@kumaraditya303 and @gvanrossum: Status check is done, and it's a failure ❌.

[miss-islington]

@kumaraditya303 and @gvanrossum: Status check is done, and it's a failure ❌.

[gvanrossum]

Why is Miss Islington spamming this PR?

[miss-islington]

@kumaraditya303 and @gvanrossum: Status check is done, and it's a failure ❌.

[miss-islington]

@kumaraditya303 and @gvanrossum: Status check is done, and it's a failure ❌.

[miss-islington]

@kumaraditya303 and @gvanrossum: Status check is done, and it's a failure ❌.

[miss-islington]

@kumaraditya303 and @gvanrossum: Status check is done, and it's a failure ❌.

[miss-islington]

@kumaraditya303 and @gvanrossum: Status check is done, and it's a failure ❌.

[miss-islington]

@kumaraditya303 and @gvanrossum: Status check is done, and it's a failure ❌.