Update golang Docker tag to v1.21 - autoclosed

This MR contains the following updates:

Package	Type	Update	Change
golang	image	minor	1.19 -> 1.21

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.gitlab-ci.yml

@@ -2,6 +2,6 @@ include: "https://git.autistici.org/ai3/build-deb/raw/master/ci-common.yml"
 
 run_tests:
   stage: test
-  image: "golang:1.20"
+  image: "golang:1.21"
   script: "go test -v ./..."