Update semgrep to current latest, by default (#20102)

This refreshes the new semgrep backend (added in #18593, in 2.19) to use
the current latest published version (`1.46.0`, instead of `1.37.0`).

The newer version of Semgrep is slightly stricter about the formatting
of the global settings file, so this inserts a dummy `anonymous_user_id`
value.

src/python/pants/backend/tools/semgrep/rules.py

@@ -154,10 +154,11 @@ async def partition(
 
 
 # We have a hard-coded settings file to side-step
-# https://github.com/returntocorp/semgrep/issues/7102, and also provide more cacheability.
+# https://github.com/returntocorp/semgrep/issues/7102, and also provide more cacheability, NB. both
+# keys are required.
 _DEFAULT_SETTINGS = FileContent(
     path="__semgrep_settings.yaml",
-    content=b"has_shown_metrics_notification: true",
+    content=b"anonymous_user_id: 00000000-0000-0000-0000-000000000000\nhas_shown_metrics_notification: true",
 )