[flake8-async] Fix examples to use async with

[MichaReiser]

Summary

Fixes #12921

[github-actions]

ruff-ecosystem results

Linter (stable)

ℹ️ ecosystem check detected linter changes. (+0 -33 violations, +0 -0 fixes in 1 projects; 53 projects unchanged)

pandas-dev/pandas (+0 -33 violations, +0 -0 fixes)

- doc/source/user_guide/style.ipynb:cell 113:31:89: E501 Line too long (90 > 88)
- doc/source/user_guide/style.ipynb:cell 113:33:89: E501 Line too long (96 > 88)
- doc/source/user_guide/style.ipynb:cell 123:3:56: E741 Ambiguous variable name: `l`
- doc/source/user_guide/style.ipynb:cell 125:2:13: C408 Unnecessary `dict` call (rewrite as a literal)
- doc/source/user_guide/style.ipynb:cell 125:4:13: C408 Unnecessary `dict` call (rewrite as a literal)
- doc/source/user_guide/style.ipynb:cell 125:6:13: C408 Unnecessary `dict` call (rewrite as a literal)
- doc/source/user_guide/style.ipynb:cell 125:8:13: C408 Unnecessary `dict` call (rewrite as a literal)
- doc/source/user_guide/style.ipynb:cell 126:1:1: NPY002 Replace legacy `np.random.seed` call with `np.random.Generator`
- doc/source/user_guide/style.ipynb:cell 126:2:1: PLW0127 Self-assignment of variable `cmap`
- doc/source/user_guide/style.ipynb:cell 126:2:8: PLW0128 Redeclared variable `cmap` in assignment
- doc/source/user_guide/style.ipynb:cell 126:3:22: NPY002 Replace legacy `np.random.randn` call with `np.random.Generator`
- doc/source/user_guide/style.ipynb:cell 128:1:22: NPY002 Replace legacy `np.random.randn` call with `np.random.Generator`
- doc/source/user_guide/style.ipynb:cell 134:1:89: E501 Line too long (93 > 88)
- doc/source/user_guide/style.ipynb:cell 141:1:89: E501 Line too long (92 > 88)
- doc/source/user_guide/style.ipynb:cell 157:1:38: F811 Redefinition of unused `f` from cell 123, line 3
- doc/source/user_guide/style.ipynb:cell 15:2:89: E501 Line too long (103 > 88)
- doc/source/user_guide/style.ipynb:cell 15:3:89: E501 Line too long (155 > 88)
- doc/source/user_guide/style.ipynb:cell 16:48:89: E501 Line too long (103 > 88)
- doc/source/user_guide/style.ipynb:cell 16:52:89: E501 Line too long (162 > 88)
... 10 additional changes omitted for rule E501
- doc/source/user_guide/style.ipynb:cell 37:1:1: NPY002 Replace legacy `np.random.seed` call with `np.random.Generator`
- doc/source/user_guide/style.ipynb:cell 37:2:20: NPY002 Replace legacy `np.random.randn` call with `np.random.Generator`
- doc/source/user_guide/style.ipynb:cell 60:1:20: NPY002 Replace legacy `np.random.randn` call with `np.random.Generator`
- doc/source/user_guide/style.ipynb:cell 6:1:27: NPY002 Replace legacy `np.random.rand` call with `np.random.Generator`
- doc/source/user_guide/style.ipynb:cell 9:1:19: NPY002 Replace legacy `np.random.randn` call with `np.random.Generator`
... 1 additional changes omitted for rule NPY002

Changes by rule (7 rules affected)

code	total	+ violation	- violation	+ fix	- fix
E501	17	0	17	0	0
NPY002	8	0	8	0	0
C408	4	0	4	0	0
E741	1	0	1	0	0
PLW0127	1	0	1	0	0
PLW0128	1	0	1	0	0
F811	1	0	1	0	0

Linter (preview)

✅ ecosystem check detected no linter changes.