Add scrape manager test for disabling staleness marker. #118

Job	Run time
Go tests with previous Go version	7m 55s
Go tests on Windows	10m 29s
Go tests	24m 50s
Build Prometheus for common architectures (0)	9m 7s
UI tests	2m 19s
Mixins tests	2m 23s
Build Prometheus for common architectures (1)	9m 19s
Build Prometheus for common architectures (2)	9m 4s
Build Prometheus for all architectures	0s
fuzzing	0s
golangci-lint	29s
codeql / Analyze (go)	24m 8s
codeql / Analyze (javascript)	1m 55s
Publish UI on npm Registry	1m 9s
Publish release artefacts	0s
Publish main branch artifacts	0s
	1h 43m 7s

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