lint: Fix semgrep scanning of extensionless Python scripts.

Semgrep 0.118.0 changed the default of --scan-unknown-extensions to
false.  It also seems that it no longer respects --lang (or never
did), so rename the config file to reflect that it only includes
Python rules, to make it clear that additional languages will require
separate config files.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

requirements/dev.in

@@ -62,7 +62,7 @@ cairosvg
 python-debian
 
 # Pattern-based lint tool
-semgrep<1.38.0  # https://github.com/returntocorp/semgrep/issues/8669
+semgrep
 
 # Contains Pysa, a security-focused static analyzer
 pyre-check

tools/lint

@@ -180,17 +180,18 @@ def run() -> None:
 
     semgrep_command = [
         "semgrep",
-        "--config=./tools/semgrep.yml",
+        "scan",
+        "--scan-unknown-extensions",
         "--error",
         "--disable-version-check",
         "--quiet",
     ]
     linter_config.external_linter(
         "semgrep-py",
-        [*semgrep_command, "--lang=python"],
+        [*semgrep_command, "--config=./tools/semgrep-py.yml"],
         ["py"],
         fix_arg="--autofix",
-        description="Syntactic grep (semgrep) code search tool (config: ./tools/semgrep.yml)",
+        description="Syntactic grep (semgrep) code search tool (config: ./tools/semgrep-py.yml)",
     )
 
     linter_config.external_linter(