Update Pydantic AI samples to the non-deprecated google: model prefix

Pydantic AI renamed the Gemini API provider prefix. google-gla: now
emits a PydanticAIDeprecationWarning and is removed in v2.0, so switch
the sample agents to the google: prefix (same free-tier Gemini API-key
flow). The gemini-2.5-flash model id is unchanged and still current.

Matches the corresponding fix in the Pydantic AI tutorial and was
flagged by a reader comment.

Author: lpozo

pydantic-ai/cats.py

@@ -2,7 +2,7 @@
 from pydantic_ai import Agent
 
 agent = Agent(
-    "google-gla:gemini-2.5-flash",
+    "google:gemini-2.5-flash",
     instructions="Help users with cat breeds. Be concise.",
 )
 

pydantic-ai/city.py

@@ -9,7 +9,7 @@ class CityInfo(BaseModel):
     fun_fact: str
 
 
-agent = Agent("google-gla:gemini-2.5-flash", output_type=CityInfo)
+agent = Agent("google:gemini-2.5-flash", output_type=CityInfo)
 
 result = agent.run_sync("Tell me about Tokyo")
 print(result.output)

pydantic-ai/first_agent.py

@@ -1,7 +1,7 @@
 from pydantic_ai import Agent
 
 agent = Agent(
-    "google-gla:gemini-2.5-flash",
+    "google:gemini-2.5-flash",
     instructions="You're a Python Expert. Reply in one sentence.",
 )
 

pydantic-ai/users.py

@@ -21,7 +21,7 @@ class UserSummary(BaseModel):
 
 
 agent = Agent(
-    "google-gla:gemini-2.5-flash",
+    "google:gemini-2.5-flash",
     output_type=UserSummary,
     deps_type=UserDatabase,
     instructions=(