Update prom/alertmanager Docker tag to v0.28.1

[renovate]

This PR contains the following updates:

Package	Update	Change
prom/alertmanager	patch	v0.28.0 -> v0.28.1

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Release Notes

prometheus/alertmanager (prom/alertmanager)

v0.28.1: 0.28.1 / 2025-03-07

Compare Source

• [ENHANCEMENT] Improved performance of inhibition rules when using Equal labels. #​4119
• [ENHANCEMENT] Improve the documentation on escaping in UTF-8 matchers. #​4157
• [ENHANCEMENT] Update alertmanager_config_hash metric help to document the hash is not cryptographically strong. #​4210
• [BUGFIX] Fix panic in amtool when using --verbose. #​4218
• [BUGFIX] Fix templating of channel field for Rocket.Chat. #​4220
• [BUGFIX] Fix rocketchat_configs written as rocket_configs in docs. #​4217
• [BUGFIX] Fix usage for --enable-feature flag. #​4214
• [BUGFIX] Trim whitespace from OpsGenie API Key. #​4195
• [BUGFIX] Fix Jira project template not rendered when searching for existing issues. #​4291
• [BUGFIX] Fix subtle bug in JSON/YAML encoding of inhibition rules that would cause Equal labels to be omitted. #​4292
• [BUGFIX] Fix header for slack_configs in docs. #​4247
• [BUGFIX] Fix weight and wrap of Microsoft Teams notifications. #​4222
• [BUGFIX] Fix format of YAML examples in configuration.md. #​4207

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