Update .NET SDK (#1473)

Update .NET SDK to version 7.0.400.

---
updated-dependencies:
- dependency-name: Microsoft.NET.Sdk
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: polly-updater-bot[bot] <138034000+polly-updater-bot[bot]@users.noreply.github.com>
Co-authored-by: polly-updater-bot[bot] <138034000+polly-updater-bot[bot]@users.noreply.github.com>

global.json

@@ -1,6 +1,6 @@
 {
   "sdk": {
-    "version": "7.0.306",
+    "version": "7.0.400",
     "allowPrerelease": false,
     "rollForward": "latestMajor"
   }