fix: issue templates syntax error

Signed-off-by: Daniel Hu <tao.hu@merico.dev>

.github/ISSUE_TEMPLATE/bug-report.yaml

@@ -1,27 +1,26 @@
----
 name: Bug Report
 description: Report a bug of DevStream
+title: "[Bug]: "
 labels: bug
----
-
 body:
 - type: textarea
   id: problem
   attributes:
-  label: What happened?
-  description: Please provide as much information as possible.
+    label: What happened?
+    description: Please provide as much information as possible.
   validations:
-  required: true
+    required: true
 
 - type: textarea
   id: repro
   attributes:
-  label: How to reproduce?
+    label: How to reproduce?
   validations:
-  required: true
+    required: true
 
 - type: textarea
   id: dtmVersion
   attributes:
-  label: DevStream version (to find out the version run: dtm version)
-  required: true
+    label: 'DevStream version (to find out the version run: dtm version)'
+  validations:
+    required: true

.github/ISSUE_TEMPLATE/documentation.yaml

@@ -1,14 +1,12 @@
----
 name: Documentation Issue
 description: Help to improve our documentation
+title: "[Docs]: "
 labels: docs
----
-
 body:
 - type: textarea
   id: problem
   attributes:
-  label: What should be changed?
-  description: Please provide as much info as possible.
+    label: What should be changed?
+    description: Please provide as much info as possible.
   validations:
-  required: true
+    required: true

.github/ISSUE_TEMPLATE/proposal.yaml

@@ -1,11 +1,12 @@
 name: Enhancement / Proposal
 description: Provide supporting details for an existing or a new feature
+title: "[Proposal]: "
 labels: proposal
 body:
 - type: textarea
   id: proposal
   attributes:
-  label: What would you like to added? Why is this needed?
-  description: |
-  For feature requests, please also engage with the PMC on Slack or WeChat.
-  required: true
+    label: What would you like to added? Why is this needed?
+    description: For feature requests, please also engage with the PMC on Slack or WeChat.
+  validations:
+    required: true