Bump fastapi from 0.79.0 to 0.81.0

Bumps [fastapi](https://github.com/tiangolo/fastapi) from 0.79.0 to 0.81.0.
- [Release notes](https://github.com/tiangolo/fastapi/releases)
- [Commits](fastapi/fastapi@0.79.0...0.81.0)

---
updated-dependencies:
- dependency-name: fastapi
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements.txt

@@ -11,7 +11,7 @@ coverage==6.4.4
 git+https://github.com/DiamondLightSource/diffcalc-core.git#egg=diffcalc-core
 distlib==0.3.6
 docutils==0.19
-fastapi==0.79.0
+fastapi==0.81.0
 filelock==3.8.0
 flake8==5.0.4
 flake8-isort==4.2.0