Fix ci_clang_tidy and ci_test_noexceptions for the BSON writer

ci_clang_tidy (modernize-use-auto) flagged the cast initialization in
bson_entry_fits(); ci_test_noexceptions aborted in the "errors at every
position" section of unit-bson.cpp, whose entries all throw, so that section
now needs exceptions like the rest of the error checks.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

tests/src/unit-bson.cpp

@@ -2357,6 +2357,8 @@ TEST_CASE("BSON written in one pass and in two passes")
         }
     }
 
+#if !defined(JSON_NOEXCEPTION)
+    // every entry here throws, which aborts without exceptions
     SECTION("errors at every position")
     {
         // an entry that cannot be written, at each place among valid ones
@@ -2395,4 +2397,5 @@ TEST_CASE("BSON written in one pass and in two passes")
             }
         }
     }
+#endif
 }