Fix mypy issues

src/serena/symbol.py

@@ -435,7 +435,7 @@ class Symbol(ToStringMixin):
         depth: int = 0,
         include_body: bool = False,
         include_children_body: bool = False,
-        include_relative_path=True,
+        include_relative_path: bool = True,
     ) -> dict[str, Any]:
         """
         Converts the symbol to a dictionary.

src/serena/util/exception.py

@@ -19,7 +19,7 @@ def is_headless_environment() -> bool:
         return False
 
     # Check for DISPLAY variable (required for X11)
-    if not os.environ.get("DISPLAY"):
+    if not os.environ.get("DISPLAY"):  # type: ignore
         return True
 
     # Check for SSH session