chore: Fix spelling

Merge https://github.com/google/adk-python/pull/2447

This PR corrects misspellings identified by the [check-spelling action](https://github.com/marketplace/actions/check-spelling)

The misspellings have been reported at https://github.com/jsoref/adk-python/actions/runs/16840838898/attempts/1#summary-47711379253

The action reports that the changes in this PR would make it happy: https://github.com/jsoref/adk-python/actions/runs/16840839269/attempts/1#summary-47711380479

Note: while I use tooling to identify errors, the tooling doesn't _actually_ provide the corrections, I'm picking them on my own. I'm a human, and I may make mistakes.

I've included a couple of changes to make CI happy. Personally, I object to CI being in a state of "random drive by person who adds a blank line in the middle of a file must fix all the preexisting bugs in the file", but that appears to be the state for this repository.

COPYBARA_INTEGRATE_REVIEW=https://github.com/google/adk-python/pull/2447 from jsoref:spelling d85398e7fd154d124d477c6af6181481a01f34e0
PiperOrigin-RevId: 827629615

tests/integration/fixture/flow_complex_spark/sample.session.json

@@ -52,7 +52,7 @@
               "response": {
                 "status": "ok",
                 "target_agent_name": "research_assistant",
-                "message": "Transfered to research_assistant"
+                "message": "Transferred to research_assistant"
               }
             }
           }
@@ -165,7 +165,7 @@
               "response": {
                 "status": "ok",
                 "target_agent_name": "spark_assistant",
-                "message": "Transfered to spark_assistant"
+                "message": "Transferred to spark_assistant"
               }
             }
           }