feat(types): Add mypy GitHub problem matcher (#19706)

.github/mypy-problem-matcher.json

@@ -0,0 +1,18 @@
+{
+    "problemMatcher": [
+        {
+            "owner": "mypy",
+            "severity": "error",
+            "pattern": [
+                {
+                    "regexp": "^([^:]*):(\\d+):(?:(\\d+):)? (?:error|note): (.*?)(?:  \\[(\\S+)\\])?$",
+                    "file": 1,
+                    "line": 2,
+                    "column": 3,
+                    "message": 4,
+                    "code": 5
+                }
+            ]
+        }
+    ]
+}

.github/workflows/ci-backend.yml

@@ -135,6 +135,9 @@ jobs:
               run: |
                   ruff format --exclude posthog/hogql/grammar --check --diff .
 
+            - name: Add Problem Matcher
+              run: echo "::add-matcher::.github/mypy-problem-matcher.json"
+
             - name: Check static typing
               run: |
                   mypy -p posthog | mypy-baseline filter