Bump docfx from 2.77.0 to 2.78.3

---
updated-dependencies:
- dependency-name: docfx
  dependency-version: 2.78.3
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

.config/dotnet-tools.json

@@ -1,10 +1,12 @@
 {
-    "version": 1,
-    "isRoot": true,
-    "tools": {
-      "docfx": {
-        "version": "2.77.0",
-        "commands": ["docfx"]
-      }
+  "version": 1,
+  "isRoot": true,
+  "tools": {
+    "docfx": {
+      "version": "2.78.3",
+      "commands": [
+        "docfx"
+      ]
     }
-  }
+  }
+}