Update dependabot.yml to include all Otel Python packages (#912)

In [this PR](#908) a new requirement.txt was added that is used only in tox test. We should update that file along this group as well.

Author: rapphil

.github/dependabot.yml

@@ -35,7 +35,7 @@ updates:
           - "@opentelemetry/*"
     rebase-strategy: "auto"
   - package-ecosystem: "pip"
-    directory: "/python/src/otel/otel_sdk"
+    directory: "/python/src/otel"
     schedule:
       interval: "weekly"
     groups: