Avoid duplication of tools list

[ericcornelissen]

Relates to #711, #741

Summary

Find a way to avoid the duplication of the list of tools between .tool-versions:

svgo-action/.tool-versions

Lines 3 to 6 in 9887768

	act 0.2.35
	actionlint 1.6.22
	cosign 1.13.1
	shellcheck 0.9.0

and nightly.yml:

svgo-action/.github/workflows/nightly.yml

Lines 30 to 33 in 9887768

	- act
	- actionlint
	- cosign
	- shellcheck