Fix the error of issue templates.

Fix the error of issue templates added by #1002 .

Author: AsakusaRinne

.github/ISSUE_TEMPLATE/blank_issue.yml

@@ -2,15 +2,11 @@ name: Blank Issue
 description: Submit an issue about Tensorflow.NET.
 labels: [Blank Issue]
 body:
-  - type: markdown
+  - type: textarea
     id: description
     attributes:
       label: Description
       description: Please describe the issue here.
       placeholder: Description
     validations:
       required: false
-  - type: markdown
-    attributes:
-      value: |
-        No matched issue template? Try the blank issue! We welcome submitting issues to Tensorflow.NET!

.github/ISSUE_TEMPLATE/bug_report.yml

@@ -7,15 +7,15 @@ body:
     attributes:
       value: |
         We welcome bug reports! Any unexpected behavior could be a BUG and this template help us gather the information to fix it.
-  - type: markdown
+  - type: textarea
     id: background
     attributes:
       label: Description
       description: Please share a clear and concise description of the problem.
       placeholder: Description
     validations:
       required: true
-  - type: markdown
+  - type: textarea
     id: repro-steps
     attributes:
       label: Reproduction Steps
@@ -24,7 +24,7 @@ body:
       placeholder: Minimal Reproduction
     validations:
       required: false
-  - type: markdown
+  - type: textarea
     id: known-workarounds
     attributes:
       label: Known Workarounds
@@ -33,7 +33,7 @@ body:
       placeholder: Known Workarounds
     validations:
       required: false
-  - type: markdown
+  - type: textarea
     id: configuration
     attributes:
       label: Configuration and Other Information
@@ -45,8 +45,4 @@ body:
           * Any other information about this problem?
       placeholder: Configuration
     validations:
-      required: false
-  - type: markdown
-    attributes:
-      value: |
-        Thanks for reporting the problem to us!
+      required: false

.github/ISSUE_TEMPLATE/feature_request.yml

@@ -7,15 +7,15 @@ body:
     attributes:
       value: |
         We welcome feature proposal/request! This template will help us gather the information we need to implement the new feature.
-  - type: markdown
+  - type: textarea
     id: background
     attributes:
       label: Background and Feature Description
       description: Please describe the purpose and value of the new feature here. If the feature is linked to a specific problem, please describe it or put the link here.
       placeholder: Purpose
     validations:
       required: true
-  - type: markdown
+  - type: textarea
     id: api-proposal
     attributes:
       label: API Definition and Usage
@@ -26,11 +26,11 @@ body:
         ```cs
         public Tensor NewFunc(Tensor x, int y);
 
-	  var result = NewFunc(input, index);
+        var result = NewFunc(input, index);
         ```
     validations:
       required: false
-  - type: markdown
+  - type: textarea
     id: alternatives
     attributes:
       label: Alternatives
@@ -39,16 +39,12 @@ body:
       placeholder: Alternatives
     validations:
       required: false
-  - type: markdown
+  - type: textarea
     id: risks
     attributes:
       label: Risks
       description: |
         Please mention any risks that to your knowledge the API proposal might entail, such as breaking changes, performance regressions, etc.
       placeholder: Risks
     validations:
-      required: false
-  - type: markdown
-    attributes:
-      value: |
-        Thanks for your contributing!
+      required: false