Fix yaml with prefixed newline broken setjob + yaml v4 (#144)

* go-yaml v3 **and** v4 workaround
* avoid yaml.Marshal broken indention

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Reviewed-on: https://gitea.com/gitea/act/pulls/144
Reviewed-by: wxiaoguang <wxiaoguang@noreply.gitea.com>
Reviewed-by: Zettat123 <zettat123@noreply.gitea.com>
Co-authored-by: Christopher Homberger <christopher.homberger@web.de>
Co-committed-by: Christopher Homberger <christopher.homberger@web.de>

pkg/jobparser/testdata/prefixed_newline.in.yaml

@@ -0,0 +1,14 @@
+name: Step with leading new line
+
+on:
+  push:
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - name: "\nExtract tag for variant"
+        id: extract_tag
+        run: |
+
+          echo Test

pkg/jobparser/testdata/prefixed_newline.out.yaml

@@ -0,0 +1,15 @@
+name: Step with leading new line
+"on":
+  push:
+jobs:
+  test:
+    name: test
+    runs-on: ubuntu-latest
+    steps:
+      - id: extract_tag
+        name: |2-
+
+          Extract tag for variant
+        run: |2
+
+          echo Test