chore(deps-dev): bump @aws-sdk/client-s3 in /backend

Bumps [@aws-sdk/client-s3](https://github.com/aws/aws-sdk-js-v3/tree/HEAD/clients/client-s3) from 3.726.1 to 3.939.0.
- [Release notes](https://github.com/aws/aws-sdk-js-v3/releases)
- [Changelog](https://github.com/aws/aws-sdk-js-v3/blob/main/clients/client-s3/CHANGELOG.md)
- [Commits](https://github.com/aws/aws-sdk-js-v3/commits/v3.939.0/clients/client-s3)

---
updated-dependencies:
- dependency-name: "@aws-sdk/client-s3"
  dependency-version: 3.939.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

backend/package.json

@@ -74,7 +74,7 @@
         "winston-loki": "^6.0.7"
     },
     "devDependencies": {
-        "@aws-sdk/client-s3": "3.726.1",
+        "@aws-sdk/client-s3": "3.939.0",
         "@jest/globals": "^30.2.0",
         "@nestjs/cli": "^11.0.10",
         "@nestjs/schematics": "^11.0.9",