Fix spelling (#3125)

include/nlohmann/json.hpp

@@ -908,7 +908,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
        - If a subtype is given and the binary array contains exactly 1, 2, 4, 8,
          or 16 elements, the fixext family (fixext1, fixext2, fixext4, fixext8)
          is used. For other sizes, the ext family (ext8, ext16, ext32) is used.
-         The subtype is then added as singed 8-bit integer.
+         The subtype is then added as signed 8-bit integer.
        - If no subtype is given, the bin family (bin8, bin16, bin32) is used.
     - BSON
        - If a subtype is given, it is used and added as unsigned 8-bit integer.
@@ -5021,7 +5021,7 @@ class basic_json // NOLINT(cppcoreguidelines-special-member-functions,hicpp-spec
           `key()` returns an empty string.
 
     @warning Using `items()` on temporary objects is dangerous. Make sure the
-             object's lifetime exeeds the iteration. See
+             object's lifetime exceeds the iteration. See
              <https://github.com/nlohmann/json/issues/2040> for more
              information.