chore(deps-dev): bump flake8 from 5.0.4 to 6.1.0 in /backend (#701)

Bumps [flake8](https://github.com/pycqa/flake8) from 5.0.4 to 6.1.0.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/PyCQA/flake8/commit/7ef0350a439c93166bc8ba89fcc3de6a9a664e6c"><code>7ef0350</code></a>
Release 6.1.0</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/354f873f8aba2b70a3757198fe10e1322bf91cb2"><code>354f873</code></a>
Merge pull request <a
href="https://github.com/pycqa/flake8/issues/1852">#1852</a>
from PyCQA/setup-cfg-fmt</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/24be8ad052b63376cf6d547ca873213015b13be5"><code>24be8ad</code></a>
Merge pull request <a
href="https://github.com/pycqa/flake8/issues/1851">#1851</a>
from PyCQA/pylint-warnings</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/5233d880696a6867b53fabf0c9d4419d83f372ad"><code>5233d88</code></a>
use setup-cfg-fmt</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/d4d1552c5b455462d6c137933d2eeb0bcd97ea81"><code>d4d1552</code></a>
Merge pull request <a
href="https://github.com/pycqa/flake8/issues/1849">#1849</a>
from PyCQA/handle-multiline-fstrings-in-312</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/cc301ed499511c56ceca3262a2302364dc146b06"><code>cc301ed</code></a>
fix pylintrc warnings</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/1ed78d592a355ece4edfee2884185dccaa732dbc"><code>1ed78d5</code></a>
handle multiline fstrings in 3.12</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/f2641954c40a48c91948304ba06a2a970bd3405e"><code>f264195</code></a>
Merge pull request <a
href="https://github.com/pycqa/flake8/issues/1850">#1850</a>
from PyCQA/312-test</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/acca35b8006e2760ceed58c1fbec34fbac024ff2"><code>acca35b</code></a>
add 3.12 to ci matrix</li>
<li><a
href="https://github.com/PyCQA/flake8/commit/579f9f6f94f3a73f1cc0910b1113962c55613f09"><code>579f9f6</code></a>
Merge pull request <a
href="https://github.com/pycqa/flake8/issues/1848">#1848</a>
from PyCQA/upgrade-pycodestyle</li>
<li>Additional commits viewable in <a
href="https://github.com/pycqa/flake8/compare/5.0.4...6.1.0">compare
view</a></li>
</ul>
</details>
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backend/dev-requirements.txt

@@ -2,7 +2,7 @@
 bandit==1.7.4
 black==23.3.0
 coverage==6.4.4
-flake8==5.0.4
+flake8==6.1.0
 isort==5.12.0
 mypy-protobuf==3.4.0
 parameterized==0.9.0