Bump albumentations in /rastervision_pytorch_learner

Bumps [albumentations](https://github.com/albumentations-team/albumentations) from 1.4.13 to 1.4.21.
- [Release notes](https://github.com/albumentations-team/albumentations/releases)
- [Commits](albumentations-team/albumentations@1.4.13...1.4.21)

---
updated-dependencies:
- dependency-name: albumentations
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

rastervision_pytorch_learner/requirements.txt

@@ -5,7 +5,7 @@ pillow==10.4.0
 torch==2.4.0
 torchvision==0.19.0
 tensorboard==2.17.0
-albumentations==1.4.13
+albumentations==1.4.21
 cython==3.0.11
 pycocotools==2.0.8
 psutil==6.0.0