chore(ci): remove Go versions below 1.24 from CI matrix

Remove CI test runs for Go 1.21.x, 1.22.x, and 1.23.x as the minimum
supported version is 1.24.0 (as defined in go.mod).

This change:
- Removes outdated Go versions from the test matrix
- Aligns CI testing with the minimum supported version
- Reduces CI execution time by removing unnecessary test runs
- Maintains testing coverage for supported versions (1.24.x, 1.25.x)

Author: claude

.github/workflows/ci.yml

@@ -38,9 +38,6 @@ jobs:
     strategy:
       matrix:
         go:
-          - 1.21.x
-          - 1.22.x
-          - 1.23.x
           - 1.24.x
           - 1.25.x