[fix][gitlab] Fix wrong issue and MR templates

.gitlab/issue_templates/template.md

 ## Description
 
 <!--
-Please describe shortly what this merge request is doing and why
-it is needed. If there is an related issue, please mention it here.
--->
+Please describe the problem/feature request. Please also describe what you want
+to achieve.
+--->
 
-## Checklist
+### Environment
 
 <!--
-Please make sure to go over all points on the checklist and
-mark them as checked.
--->
+Please provide information about the operating system and relevant versions of
+the software.
 
-- [ ] I made sure that the source files are formatted properly.
-- [ ] I added my changes to the changelog (`CHANGELOG.md`)
-- [ ] I updated the documentation.
+Example:
+Ubuntu 20.04 LTS, preCICE 2.3.0, DuMuX 3.4, DuMuX-preCICE 0.1
+--->
 
-<!--
-If the pull request adds new content, please check the points
-below. Otherwise remove the following lines.
--->
+## Steps to reproduce
+
+<!-- Please describe the steps one has to execture to reproduce the problem. --->
+
+### Expected behavior
+
+<!-- What outcome did you expect? --->
+
+### Actual behavior
 
-- [ ] I added a test for the new feature.
+<!-- What was the actual outcome? --->

.gitlab/merge_request_templates/template.md

 ## Description
 
 <!--
-Please describe the problem/feature request. Please also describe what you want
-to achieve.
---->
+Please describe shortly what this merge request is doing and why
+it is needed. If there is an related issue, please mention it here.
+-->
 
-### Environment
+## Checklist
 
 <!--
-Please provide information about the operating system and relevant versions of
-the software.
+Please make sure to go over all points on the checklist and
+mark them as checked.
+-->
 
-Example:
-Ubuntu 20.04 LTS, preCICE 2.3.0, DuMuX 3.4, DuMuX-preCICE 0.1
---->
+- [ ] I made sure that the source files are formatted properly.
+- [ ] I added my changes to the changelog (`CHANGELOG.md`)
+- [ ] I updated the documentation.
 
-## Steps to reproduce
-
-<!-- Please describe the steps one has to execture to reproduce the problem. --->
-
-### Expected behavior
-
-<!-- What outcome did you expect? --->
-
-### Actual behavior
+<!--
+If the pull request adds new content, please check the points
+below. Otherwise remove the following lines.
+-->
 
-<!-- What was the actual outcome? --->
+- [ ] I added a test for the new feature.