More ResourceWarnings fixes

src/ZODB/FileStorage/FileStorage.py

@@ -962,10 +962,9 @@ class FileStorage(
                             # We're undoing a blob modification operation.
                             # We have to copy the blob data
                             tmp = ZODB.utils.mktemp(dir=self.fshelper.temp_dir)
-                            with open(tmp, 'wb') as fp:
-                                ZODB.utils.cp(
-                                    self.openCommittedBlobFile(h.oid, userial),
-                                    fp)
+                            with self.openCommittedBlobFile(h.oid, userial) as sfp:
+                                with open(tmp, 'wb') as dfp:
+                                    ZODB.utils.cp(sfp, dfp)
                             self._blob_storeblob(h.oid, self._tid, tmp)
 
                 new = DataHeader(h.oid, self._tid, ipos, otloc, 0, len(p))

src/ZODB/tests/IExternalGC.test

@@ -68,7 +68,7 @@ We can still get the data if we load before the time we deleted.
     True
     >>> storage.loadBefore(oid1, conn.root()._p_serial) == (p1, s1, tid)
     True
-    >>> open(storage.loadBlob(oid1, s1)).read()
+    >>> with open(storage.loadBlob(oid1, s1)) as fp: fp.read()
     'some data'
 
 If we pack, however, the old data will be removed and the data will be