Fix class FluentBundle parameter "functions" typing #43

Job	Run time
lint	16s
compatibility (./fluent.syntax)	1s
compatibility (fluent.syntax==0.19.0)	1s
compatibility (fluent.syntax==0.18.1 six)	1s
compatibility (fluent.syntax==0.17.0 six)	1s
test (ubuntu-22.04, 3.11)	13s
test (ubuntu-22.04, 3.8)	21s
test (windows-2022, 3.8)	1m 4s
test (ubuntu-22.04, 3.12)	13s
test (ubuntu-22.04, 3.9)	18s
test (ubuntu-22.04, pypy3.10)	31s
test (windows-2022, pypy3.9)	45s
test (ubuntu-22.04, pypy3.9)	23s
test (ubuntu-22.04, 3.10)	19s
test (windows-2022, 3.9)	32s
test (windows-2022, 3.10)	33s
test (windows-2022, 3.7)	2m 12s
test (windows-2022, 3.12)	35s
test (ubuntu-22.04, 3.7)	26s
test (windows-2022, pypy3.10)	43s
test (windows-2022, 3.11)	35s
	10m 3s

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