Update grafana/mimir Docker tag to v3.1.4

[renovate]

This PR contains the following updates:

Package	Update	Change
grafana/mimir (source)	patch	3.1.2 → 3.1.4

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Release Notes

grafana/mimir (grafana/mimir)

v3.1.4

Grafana Mimir

• [BUGFIX] Packaging: Fix the DEB/RPM packages shipping the mimir, mimirtool, metaconvert, and query-tee binaries without the executable bit set, which caused mimir.service to fail to start. #​16166

v3.1.3

Grafana Mimir

• [BUGFIX] Fix build failure on Windows and FreeBSD due to reference leaks instrumentation code. Enabling reference leaks instrumentation in those platforms now causes a configuration validation error instead. #​15837
• [BUGFIX] Upgrade Go to 1.26.5 to address CVE-2026-39822 and CVE-2026-42505. #​16078

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