fix(deps): update module github.com/slack-go/slack to v0.21.0

Author: renovate[bot]

go.mod

@@ -7,7 +7,7 @@ require (
 	github.com/expr-lang/expr v1.17.8
 	github.com/hashicorp/vault/api v1.23.0
 	github.com/panjf2000/gnet/v2 v2.9.7
-	github.com/slack-go/slack v0.20.0
+	github.com/slack-go/slack v0.21.0
 	github.com/spf13/cobra v1.10.2
 	github.com/spf13/viper v1.21.0
 	github.com/stretchr/testify v1.11.1

go.sum

@@ -96,6 +96,8 @@ github.com/slack-go/slack v0.19.0 h1:J8lL/nGTsIUX53HU8YxZeI3PDkA+sxZsFrI2Dew7h44
 github.com/slack-go/slack v0.19.0/go.mod h1:K81UmCivcYd/5Jmz8vLBfuyoZ3B4rQC2GHVXHteXiAE=
 github.com/slack-go/slack v0.20.0 h1:gbDdbee8+Z2o+DWx05Spq3GzbrLLleiRwHUKs+hZLSU=
 github.com/slack-go/slack v0.20.0/go.mod h1:K81UmCivcYd/5Jmz8vLBfuyoZ3B4rQC2GHVXHteXiAE=
+github.com/slack-go/slack v0.21.0 h1:TAGnZYFp79LAG/oqFzYhFJ9LwEwXJ93heCkPvwjxc7o=
+github.com/slack-go/slack v0.21.0/go.mod h1:K81UmCivcYd/5Jmz8vLBfuyoZ3B4rQC2GHVXHteXiAE=
 github.com/spf13/afero v1.15.0 h1:b/YBCLWAJdFWJTN9cLhiXXcD7mzKn9Dm86dNnfyQw1I=
 github.com/spf13/afero v1.15.0/go.mod h1:NC2ByUVxtQs4b3sIUphxK0NioZnmxgyCrfzeuq8lxMg=
 github.com/spf13/cast v1.10.0 h1:h2x0u2shc1QuLHfxi+cTJvs30+ZAHOGRic8uyGTDWxY=