gh-38624: Fix issue report formatting
Currently the bug report and failure to build report issue templates
have the environment sections set to render as Markdown. Rather than
actually rendering this as Markdown, GitHub renders these as Markdown
source code which I imagine is not what was intended for these
templates. This PR removes the instructions to render as Markdown source
code, which has the effect of the section rendering as processed
Markdown.
Examples of current formatting:
https://github.com/vincentmacri/sage/issues/6
https://github.com/vincentmacri/sage/issues/7
Examples of new proposed formatting:
https://github.com/vincentmacri/sage/issues/3
https://github.com/vincentmacri/sage/issues/5
### :memo: Checklist
<!-- Put an `x` in all the boxes that apply. -->
- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [ ] I have linked a relevant issue or discussion.
- [ ] I have created tests covering the changes.
- [ ] I have updated the documentation and checked the documentation
preview.
### :hourglass: Dependencies
None
URL: https://github.com/sagemath/sage/pull/38624
Reported by: Vincent Macri
Reviewer(s): Kwankyu Lee, Vincent Macri
