Fix dependabot.yml indentation and quoting

Correct YAML list indentation and normalize string quoting in .github/dependabot.yml (use two-space list indent and single quotes). This ensures the updates entry for the devcontainers package-ecosystem is parsed correctly by Dependabot.

Author: bradpotts

.github/dependabot.yml

@@ -6,7 +6,7 @@
 
 version: 2
 updates:
- - package-ecosystem: "devcontainers"
-   directory: "/"
-   schedule:
-     interval: weekly
+  - package-ecosystem: 'devcontainers'
+    directory: '/'
+    schedule:
+      interval: weekly