Update module github.com/prometheus/client_golang to v1.20.4

This MR contains the following updates:

Package	Type	Update	Change
github.com/prometheus/client_golang	require	patch	v1.20.3 -> v1.20.4

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Release Notes

prometheus/client_golang (github.com/prometheus/client_golang)

v1.20.4

Compare Source

• [BUGFIX] histograms: Fix a possible data race when appending exemplars vs metrics gather. #​1623

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