Support fcntl check on Emscripten (#398)

* Support fcntl check on Emscripten

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Fix `fcntl.flock` typo

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: juntyr

src/filelock/_unix.py

@@ -26,7 +26,9 @@ def _release(self) -> None:
 else:  # pragma: win32 no cover
     try:
         import fcntl
-    except ImportError:
+
+        _ = (fcntl.flock, fcntl.LOCK_EX, fcntl.LOCK_NB, fcntl.LOCK_UN)
+    except (ImportError, AttributeError):
         pass
     else:
         has_fcntl = True