test

Add docs for new `@mustBeConst` diagnostic (#5689) #705

Job	Run time
Validate Firebase configuration	22s
Build site and check links	1m 9s
Check if code excerpts are up to date	39s
Analyze and test code examples (beta, false)	2m 50s
Analyze and test code examples (stable, false)	3m 40s
	8m 40s

Provide feedback