Update Black tests (#20794)

Summary
--

```shell
git clone git@github.com:psf/black.git ../other/black
crates/ruff_python_formatter/resources/test/fixtures/import_black_tests.py ../other/black
```

Then ran our tests and accepted the snapshots

I had to make a small fix to our tuple normalization logic for `del`
statements
in the second commit, otherwise the tests were panicking at a changed
AST. I
think the new implementation is closer to the intention described in the
nearby
comment anyway, though.

The first commit adds the new Python, settings, and `.expect` files, the
next three commits make some small
fixes to help get the tests running, and then the fifth commit accepts
all but one of the new snapshots. The last commit includes the new
unsupported syntax error for one f-string example, tracked in #20774.

Test Plan
--

Newly imported tests. I went through all of the new snapshots and added
review comments below. I think they're all expected, except a few cases
I wasn't 100% sure about.

crates/ruff_python_formatter/tests/normalizer.rs

@@ -1,8 +1,5 @@
+use regex::Regex;
 use std::sync::LazyLock;
-use {
-    itertools::Either::{Left, Right},
-    regex::Regex,
-};
 
 use ruff_python_ast::{
     self as ast, BytesLiteralFlags, Expr, FStringFlags, FStringPart, InterpolatedStringElement,
@@ -46,18 +43,9 @@ impl Transformer for Normalizer {
     fn visit_stmt(&self, stmt: &mut Stmt) {
         if let Stmt::Delete(delete) = stmt {
             // Treat `del a, b` and `del (a, b)` equivalently.
-            delete.targets = delete
-                .targets
-                .clone()
-                .into_iter()
-                .flat_map(|target| {
-                    if let Expr::Tuple(tuple) = target {
-                        Left(tuple.elts.into_iter())
-                    } else {
-                        Right(std::iter::once(target))
-                    }
-                })
-                .collect();
+            if let [Expr::Tuple(tuple)] = delete.targets.as_slice() {
+                delete.targets = tuple.elts.clone();
+            }
         }
 
         transformer::walk_stmt(self, stmt);