Update .drone.yml

remove run on push, bump image to 3.13

.drone.yml

@@ -4,11 +4,11 @@ type: docker
 name: python-ci
 
 trigger:
-  event: [ push, pull_request ]
+  event: [ pull_request ]
 
 steps:
   - name: setup+deps
-    image: python:3.12-slim
+    image: python:3.13-slim
     environment:
       UV_NO_SYNC_PROGRESS: "1"
     commands:
@@ -32,7 +32,7 @@ steps:
       - uv pip install pytest pytest-cov mypy ruff
 
   - name: lint-typecheck
-    image: python:3.12-slim
+    image: python:3.13-slim
     commands:
       - export PATH="$HOME/.local/bin:$PATH"
       - . .venv/bin/activate
@@ -40,7 +40,7 @@ steps:
       - mypy --ignore-missing-imports .
 
   - name: test
-    image: python:3.12-slim
+    image: python:3.13-slim
     commands:
       - export PATH="$HOME/.local/bin:$PATH"
       - . .venv/bin/activate