Update issue templates

.github/ISSUE_TEMPLATE/bug_report.md

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+---
+name: Bug report
+about: Create a report to help us improve
+title: ''
+labels: ''
+assignees: ''
+
+---
+
+**Description**
+
+_Example:_ There are hundreds of error messages in the UTBot log. Looks like the problem is in the concrete executor.
+
+**To Reproduce**
+
+Steps to reproduce the behavior:
+
+_Example:_
+
+1. Run the 'X' project in IntelliJ Idea
+2. Use plugin to generate tests
+3. Open the generated test
+
+**Expected behavior**
+
+_Example:_ Tests are supposed to be generated.
+
+**Actual behavior**
+
+_Example:_ An error test is generated with information about errors in the concrete executor.
+
+**Visual proofs (screenshots, logs, images)**
+
+_Example:_
+~~~
+public void testFail_errors() {
+// Couldn't generate some tests. List of errors:
+//
+// 684 occurrences of:
+// Concrete execution failed
+}
+~~~
+
+**Environment**
+
+Test framework:
+
+Java:
+
+Mockito:
+
+ - [ ] Other packages
+ - [ ] Other classes
+ - [ ] Static mocking
+
+Test:
+
+- [ ] Parametrized
+
+**Additional context**
+
+Add any other context about the problem here.