Add new prompty unit test for Mustache #31

Job	Run time
run unit tests on supported python versions (3.9, ubuntu-latest)	1m 8s
run unit tests on supported python versions (3.9, macOS-latest)	1m 5s
run unit tests on supported python versions (3.9, windows-latest)	1m 43s
run unit tests on supported python versions (3.10, ubuntu-latest)	1m 7s
run unit tests on supported python versions (3.10, macOS-latest)	57s
run unit tests on supported python versions (3.10, windows-latest)	1m 54s
run unit tests on supported python versions (3.11, ubuntu-latest)	59s
run unit tests on supported python versions (3.11, macOS-latest)	39s
run unit tests on supported python versions (3.11, windows-latest)	2m 8s
run unit tests on supported python versions (3.12, ubuntu-latest)	1m 9s
run unit tests on supported python versions (3.12, macOS-latest)	42s
run unit tests on supported python versions (3.12, windows-latest)	1m 47s
run unit tests on supported python versions (3.13, ubuntu-latest)	1m 2s
run unit tests on supported python versions (3.13, macOS-latest)	38s
run unit tests on supported python versions (3.13, windows-latest)	2m 0s
	18m 58s

Provide feedback