Apparently, that was a bashism

.gitlab-ci.yml

@@ -17,8 +17,8 @@ test_2:
   stage: test
   before_script:
      # Authenticate using the keytab:
-    - apk update && apk add make krb5
-    - base64 --decode <(echo "$KRB_KEYTAB_CONTENTS") > $KRB_USERNAME.keytab
+    - apk update && apk add make krb5 bash
+    - bash -c "base64 --decode <(echo \"$KRB_KEYTAB_CONTENTS\") > $KRB_USERNAME.keytab"
     - kinit $KRB_USERNAME@CERN.CH -k -t $KRB_USERNAME.keytab
   script:
     - pip install -r requirements.txt
@@ -31,9 +31,9 @@ test_3:
   stage: test
   image: frolvlad/alpine-python3
   before_script:
-    - apk update && apk add make krb5
+    - apk update && apk add make krb5 bash
      # Authenticate using the keytab:
-    - base64 --decode <(echo "$KRB_KEYTAB_CONTENTS") > $KRB_USERNAME.keytab
+    - bash -c "base64 --decode <(echo \"$KRB_KEYTAB_CONTENTS\") > $KRB_USERNAME.keytab"
     - kinit $KRB_USERNAME@CERN.CH -k -t $KRB_USERNAME.keytab
   script:
     - pip install -r requirements.txt