Add dependabot update checking for GitHub actions

[imciner2]

This is just a copy of the dependabot config in the OSQP repo.

[coveralls]

Pull Request Test Coverage Report for Build 8940020969

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 100.0%

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Totals
Change from base Build 8940015207:	0.0%
Covered Lines:	87
Relevant Lines:	87

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💛 - Coveralls