Renovate: Update module github.com/prometheus/client_golang to v1.21.1

[renovate]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
github.com/prometheus/client_golang	v1.21.0 -> v1.21.1

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Release Notes

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

v1.21.1: / 2025-03-04

Compare Source

This release addresses a major performance regression introduced in #​1661 -- thanks to all who reported this quickly:
@​chlunde, @​dethi, @​aaronbee @​tsuna 💪🏽. This patch release also fixes the iOS build.

We will be hardening the release process even further (#​1759, #​1761) to prevent this in future, sorry for the inconvenience!

The high concurrency optimization is planned to be eventually reintroduced, however in a much safer manner, potentially in a separate API.

• [BUGFIX] prometheus: Revert of Inc, Add and Observe cumulative metric CAS optimizations (#​1661), causing regressions on low concurrency cases #​1757
• [BUGFIX] prometheus: Fix GOOS=ios build, broken due to process_collector_* wrong build tags. #​1758

All commits

• Revert "exponential backoff for CAS operations on floats" and cut 1.21.1 by @​bwplotka in https://github.com/prometheus/client_golang/pull/1757
• Fix ios build for 1.21.1 by @​bwplotka in https://github.com/prometheus/client_golang/pull/1758

Full Changelog: prometheus/client_golang@v1.21.0...v1.21.1

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