Add default version to `version_string` function #4124

Job	Run time
Check Access Permissions	3s
Check Packages and Shards	1m 27s
Mutation Testing - Normal, Stackslib	2h 40m 51s
Mutation Testing - Normal, Small	0s
Mutation Testing - Shards, Small	0s
Mutation Testing - Normal, Stacks Node	21m 45s
Mutation Testing - Shards, Stackslib	0s
Mutation Testing - Shards, Stacks Node	0s
Mutation Testing - Normal, Stacks Signer	0s
Output Mutants	5s
	3h 4m 11s

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