Rollup merge of #138656 - Kobzol:post-merge-unnest, r=marcoieni

Remove double nesting in post-merge workflow

See [this](rust-lang/rust#138630 (comment)) :)

Can be tested with:
```bash
#!/bin/bash

PARENT_COMMIT=493c38ba371929579fe136df26eccd9516347c7a
SHA=259fdb521200c9abba547302fc2c826479ef26b2

printf "<details>\n<summary>What is this?</summary>\n" >> output.log
printf "This is an experimental post-merge analysis report that shows differences in test outcomes between the merged PR and its parent PR.\n" >> output.log
printf "</details>\n\n" >> output.log

cargo run --release post-merge-report ${PARENT_COMMIT} ${SHA} >> output.log
```

I think that it's better to leave the notice in CI, to avoid generating it in citool, which can also be executed locally.

r? `@marcoieni`

Author: matthiaskrgr