print MDTEST_TEST_FILTER value in single-quotes (and escaped) (#16548)

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## Summary

<!-- What's the purpose of the change? What does it do, and why? -->

If an mdtest fails, the error output will include an example command
that can be run to re-run just the failing test, e.g

```
To rerun this specific test, set the environment variable: MDTEST_TEST_FILTER="sync.md - With statements - Context manager with non-callable `__exit__` attribute"
MDTEST_TEST_FILTER="sync.md - With statements - Context manager with non-callable `__exit__` attribute" cargo test -p red_knot_python_semantic --test mdtest -- mdtest__with_sync
```
This is very helpful, but because we're printing the envvar value
surrounded in double-quotes, the bits between backticks in this example
get interpreted as a shell interpolation. When running this in zsh, for
example, I see

```console
❯ MDTEST_TEST_FILTER="sync.md - With statements - Context manager with non-callable `__exit__` attribute" cargo test -p red_knot_python_semantic --test mdtest -- mdtest__with_sync  
zsh: command not found: __exit__
   Compiling red_knot_python_semantic v0.0.0 (/home/ericmarkmartin/Development/ruff/crates/red_knot_python_semantic)
   Compiling red_knot_test v0.0.0 (/home/ericmarkmartin/Development/ruff/crates/red_knot_test)
    Finished `test` profile [unoptimized + debuginfo] target(s) in 6.09s
     Running tests/mdtest.rs (target/debug/deps/mdtest-149b8f9d937e36bc)

running 1 test
test mdtest__with_sync ... ok
```
[^1]

This is a minor annoyance which we can solve by using single-quotes
instead of double-quotes for this string. To do so safely, we also
escape single-quotes possibly contained within the string.

There is a [shell-quote](https://github.com/allenap/shell-quote) crate,
which seems to handle all this escaping stuff for you but fixing this
issue perfectly isn't a big deal (if there are more things to escape we
can deal with it then), so adding a new dependency (even a dev one)
seemed overkill.

[^1]: The filter does still work---it turns out that the filter
`MDTEST_TEST_FILTER="sync.md - With statements - Context manager with
non-callable attribute"` (what you get after the failed interpolation)
is still good enough

## Test Plan
<!-- How was it tested? -->

I broke the ``## Context manager with non-callable `__exit__`
attribute`` test by deleting the error assertion, then successfully ran
the new command it printed out.

crates/red_knot_test/src/lib.rs

@@ -79,13 +79,13 @@ pub fn run(
                 }
             }
 
+            let escaped_test_name = test.name().replace('\'', "\\'");
+
             println!(
-                "\nTo rerun this specific test, set the environment variable: {MDTEST_TEST_FILTER}=\"{}\"",
-                test.name()
+                "\nTo rerun this specific test, set the environment variable: {MDTEST_TEST_FILTER}='{escaped_test_name}'",
             );
             println!(
-                "{MDTEST_TEST_FILTER}=\"{}\" cargo test -p red_knot_python_semantic --test mdtest -- {test_name}",
-                test.name()
+                "{MDTEST_TEST_FILTER}='{escaped_test_name}' cargo test -p red_knot_python_semantic --test mdtest -- {test_name}",
             );
         }
     }