Add alpine 3.21 support #4821

Job	Run time
Unit tests with race condition detection	2m 26s
Lint	4m 18s
Unit Tests	2m 3s
Build Unsigned Snapshot	1m 53s
Performance Tests	4m 46s
Integration Tests - Official OSS Images (bookworm, stable, debian)	6m 8s
Load Tests	4m 33s
Integration Tests - Official OSS Images (bookworm, mainline, debian)	6m 15s
Integration Tests (ubuntu, 22.04)	9m 9s
Integration Tests - Official Plus Images (alpine, 3.21, r33, alpine, /nginx-plus/agent)	1m 47s
Integration Tests - Official OSS Images (alpine, stable, alpine)	6m 0s
Integration Tests (redhatenterprise, 9)	8m 33s
Integration Tests - Official OSS Images (alpine, mainline, alpine)	5m 50s
Integration Tests - Official Plus Images (alpine, 3.20, r32, alpine, /nginx-plus/agent)	2m 5s
Integration Tests (alpine, 3.19)	7m 18s
Integration Tests - Official Plus Images (alpine, 3.19, r31, alpine, /nginx-plus/agent)	2m 6s
Integration Tests - Official Plus Images (debian, bookworm, r32, debian, /nginx-plus/agent)	2m 5s
Integration Tests - Official Plus Images (debian, bookworm, r31, debian, /nginx-plus/agent)	2m 5s
Publish NGINX Agent v3 packages	0s
	1h 19m 20s

Provide feedback