style: edtlib: Use the more readable not-equal operator

Replace 'not xx == xx' with 'xx != xx' to
fix the Ruff SIM201 warning.

Signed-off-by: James Roy <rruuaanng@outlook.com>

.ruff-excludes.toml

@@ -436,7 +436,6 @@
     "UP035",    # https://docs.astral.sh/ruff/rules/deprecated-import
 ]
 "./scripts/dts/python-devicetree/src/devicetree/dtlib.py" = [
-    "SIM201",   # https://docs.astral.sh/ruff/rules/negate-equal-op
     "UP007",    # https://docs.astral.sh/ruff/rules/non-pep604-annotation
 ]
 "./scripts/dts/python-devicetree/src/devicetree/edtlib.py" = [

scripts/dts/python-devicetree/src/devicetree/dtlib.py

@@ -110,7 +110,7 @@ class Node:
 
         if name.count("@") > 1:
             dt._parse_error("multiple '@' in node name")
-        if not name == "/":
+        if name != "/":
             for char in name:
                 if char not in _nodename_chars:
                     dt._parse_error(f"{self.path}: bad character '{char}' "