fix(tests): Fix race condition causing flakiness in PHP generator test (#6213)
fix(tests): Fix race condition causing flakiness in PHP generator test (#6213)

Turns out process.exit() was sometimes getting called before the
(async) fs.writeFile had finished writing the last of the generator
output files.
google/blockly,google/blockly,google/blockly,rachel-fenichel/blockly,google/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,google/blockly,rachel-fenichel/blockly,google/blockly,google/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly,rachel-fenichel/blockly