hghave: detect newer pylint

Older versions (e.g. 2.7.2) say: "Usage: pylint [options]"

Newer versions (e.g. 2.15.5) say: "usage: pylint [options]"

tests/hghave.py

@@ -612,7 +612,7 b' def has_pyflakes():'
 
 @check("pylint", "Pylint python linter")
 def has_pylint():
-    return matchoutput("pylint --help", br"Usage:[ ]+pylint", True)
+    return matchoutput("pylint --help", br"[Uu]sage:[ ]+pylint", True)
 
 
 @check("clang-format", "clang-format C code formatter (>= 11)")