ci: Fix formatting

At the same time, reduce indentation level on lists because otherwise the formatter is broken.

.gitlab-ci.yml

@@ -1,15 +1,15 @@
 image: debian:bullseye
 
 stages:
-  - build
-  - test
+- build
+- test
 
 before_script:
-  - apt-get -y update
-  - apt-get -y install wget ca-certificates gnupg
-  - echo "deb [trusted=yes] http://ci.puri.sm/ bullseyeci main" > /etc/apt/sources.list.d/ci.list
-  - wget -O- https://ci.puri.sm/ci-repo.key | apt-key add -
-  - apt-get -y update
+- apt-get -y update
+- apt-get -y install wget ca-certificates gnupg
+- echo "deb [trusted=yes] http://ci.puri.sm/ bullseyeci main" > /etc/apt/sources.list.d/ci.list
+- wget -O- https://ci.puri.sm/ci-repo.key | apt-key add -
+- apt-get -y update
 
 build_docs:
   stage: build

tools/yamlfmt

@@ -4,7 +4,8 @@
 Usage: yamlfmt.py [--apply] file.yaml
 """
 
-import ruamel.yaml
+import io
+from ruamel.yaml import YAML
 import sys
 
 args = sys.argv[:]
@@ -16,10 +17,16 @@ except ValueError:
 
 path = args[1]
 
+def dump(yaml, yml):
+    buf = io.BytesIO()
+    yaml.dump(yml, buf)
+    return buf.getvalue().decode('utf-8')
+
 with open(path) as f:
     contents = f.read()
-    yml = ruamel.yaml.round_trip_load(contents)
-    formatted = ruamel.yaml.round_trip_dump(yml, block_seq_indent=2)
+    yaml = YAML()
+    yml = yaml.load(contents)
+    formatted = dump(yaml, yml)
     well_formatted = formatted == contents
         
 if not well_formatted: