fix: remove Poetry 1.5.1 pin on Linux, use latest

Poetry 1.5.1 cannot read lock files generated by Poetry 2.x,
causing CI lint step to fail.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: wu-sheng

Makefile

@@ -47,7 +47,7 @@ else ifeq ($(OS),Darwin)
 	-curl -sSL https://install.python-poetry.org | python3 -
 	poetry self update || $(MAKE) poetry-fallback
 else
-	-curl -sSL https://install.python-poetry.org | python3 - --version 1.5.1
+	-curl -sSL https://install.python-poetry.org | python3 -
 endif
 
 .PHONY: gen