issue templates: add "I'm not sure" option to dropdowns

Author: SableRaf

.github/ISSUE_TEMPLATE/1_bug_report.yml

@@ -11,6 +11,7 @@ body:
     description: You may select more than one.
     multiple: true
     options:
+        - I'm not sure
         - Accessibility
         - Core/Environment/Rendering
         - PDE

.github/ISSUE_TEMPLATE/2_enhancement.yml

@@ -16,6 +16,7 @@ body:
     description: Choose the most relevant area for the proposed feature or improvement.
     multiple: true
     options:
+        - I'm not sure
         - Accessibility
         - Core/Environment/Rendering
         - PDE

.github/ISSUE_TEMPLATE/3_feature-request.yml

@@ -16,6 +16,7 @@ body:
     description: Choose the sub-area most relevant to your feature request.
     multiple: true
     options:
+      - I'm not sure
       - Accessibility
       - Core/Environment/Rendering
       - PDE