ci: add go-fuzz tag to build and test command

This commit adds `-tag gofuzz` to the build and
test commands to ensure that also fuzzing code
compiles and any testing using fuzzing works.

Author: Andreas Auernhammer

.cirrus.yml

@@ -12,6 +12,6 @@ task:
        - diff -au <(go vet .) <(printf "")
    get_script:
       - go get ./...
-      - go build ./...
-   test_script: go test ./...
+      - go build -tags gofuzz ./...
+   test_script: go test -tags gofuzz ./...