Co-authored-by: Sam Bull <[email protected]>
(cherry picked from commit 7108d64)

…_cookies (#8537)

**This is a backport of PR #8535 as merged into master
(7108d64).**


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## What do these changes do?
 
Small speed up to cookiejar

Using `str.format` is ~16% faster than the lambda

followup to
#7944 (comment). I
was hoping to use `join` there but later realized `str.format` will take
`*args`

## Are there changes in behavior for the user?

no
## Is it a substantial burden for the maintainers to support this?

no


benchmark
```python
import timeit
import itertools

_FORMAT_PATH = "{0}/{1}".format

path = "lolonglonglonglonglonglongng/path/to/a/file"

print(
    timeit.timeit(
        'itertools.accumulate(path.split("/"), _FORMAT_PATH)', globals=globals()
    )
)


print(
    timeit.timeit(
        'itertools.accumulate(path.split("/"), lambda x, y: f"{x}/{y}")',
        globals=globals(),
    )
)
```

Co-authored-by: J. Nick Koston <[email protected]>