Replace + Array Union Operator with array_merge

[ghostwriter]

Fix #1323 - https://3v4l.org/JFpUQ

The + operator returns the right-hand array appended to the left-hand array; for keys that exist in both arrays, the elements from the left-hand array will be used, and the matching elements from the right-hand array will be ignored.

https://www.php.net/manual/en/language.operators.array.php

Merges the elements of one or more arrays together so that the values of one are appended to the end of the previous one. It returns the resulting array.

If the input arrays have the same string keys, then the later value for that key will overwrite the previous one. If, however, the arrays contain numeric keys, the later value will not overwrite the original value, but will be appended.

Values in the input arrays with numeric keys will be renumbered with incrementing keys starting from zero in the result array.

https://www.php.net/manual/en/function.array-merge.php

[codecov]

Codecov Report

Merging #1324 (818cb89) into 1.6.x (68782e9) will not change coverage.
The diff coverage is 0.00%.

Additional details and impacted files

@@            Coverage Diff            @@
##              1.6.x    #1324   +/-   ##
=========================================
  Coverage     77.88%   77.88%           
  Complexity     1014     1014           
=========================================
  Files            76       76           
  Lines          2595     2595           
=========================================
  Hits           2021     2021           
  Misses          574      574           

Files Changed	Coverage Δ
library/Mockery/Reflector.php	94.01% <0.00%> (ø)