fix(tests): update crashtracker_segfault EXPECTF for libdatadog 1.6 schema

- runtime_stack moved to message.experimental.runtime_stack
- new error block with native crash stack (Datadog Crashtracker 1.0 format)
- data_schema_version bumped to 1.6
- signal message changed to "Process terminated with SI_USER (SIGSEGV)"

Author: Leiyks

tests/ext/crashtracker_segfault.phpt

@@ -70,10 +70,20 @@ $rr->waitForRequest(function ($request) {
 %A{
     "message": {
 %A
+        "data_schema_version": "1.6",
         "error": {
-%A
+            "is_crash": true,
+            "kind": "UnixSignal",
+            "message": "Process terminated with SI_USER (SIGSEGV)",
+            "thread_name": "%s",
             "source_type": "Crashtracking",
+            "stack": {
+                "format": "Datadog Crashtracker 1.0",
+                "frames": [
 %A
+                ],
+                "incomplete": false
+            }
         },
         "experimental": {
             "runtime_stack": {
@@ -101,6 +111,9 @@ $rr->waitForRequest(function ($request) {
                 ]
             }
         },
+        "files": {
+%A
+        },
 %A
         "incomplete": false,
         "metadata": {