build: update Gin minimum Go version to 1.21 #1490

Job	Run time
lint	18s
ubuntu-latest @ Go 1.21	48s
ubuntu-latest @ Go 1.21 -tags nomsgpack	34s
ubuntu-latest @ Go 1.21 -tags "sonic avx"	59s
ubuntu-latest @ Go 1.21 -tags go_json	44s
ubuntu-latest @ Go 1.21 -race	12s
ubuntu-latest @ Go 1.22	37s
ubuntu-latest @ Go 1.22 -tags nomsgpack	39s
ubuntu-latest @ Go 1.22 -tags "sonic avx"	56s
ubuntu-latest @ Go 1.22 -tags go_json	50s
ubuntu-latest @ Go 1.22 -race	24s
macos-latest @ Go 1.21	48s
macos-latest @ Go 1.21 -tags nomsgpack	49s
macos-latest @ Go 1.21 -tags "sonic avx"	45s
macos-latest @ Go 1.21 -tags go_json	46s
macos-latest @ Go 1.21 -race	21s
macos-latest @ Go 1.22	41s
macos-latest @ Go 1.22 -tags nomsgpack	35s
macos-latest @ Go 1.22 -tags "sonic avx"	46s
macos-latest @ Go 1.22 -tags go_json	50s
macos-latest @ Go 1.22 -race	26s
	13m 48s

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