Fix bad code block formatting in docs

I noticed that
<https://sw.kovidgoyal.net/kitty/conf/#opt-kitty.text_fg_override_threshold>
said ':code:` ratio`' instead of being formatted as code. I assume
that's because of a space after `.

Fixed 2 cases where I found the issue.
Added a simple code block check to CI.

Signed-off-by: Galantsev, Dmitrii <dmitrii.galantsev@amd.com>

.github/workflows/ci.yml

@@ -81,6 +81,9 @@ jobs:
           - name: Test for trailing whitespace
             run: if grep -Inr '\s$' kitty kitty_tests kittens docs *.py *.asciidoc *.rst *.go .gitattributes .gitignore; then echo Trailing whitespace found, aborting.; exit 1; fi
 
+          - name: Test for bad code block formatting
+            run: if grep -Inr ':code:`\s' kitty kitty_tests kittens docs *.py *.asciidoc *.rst *.go .gitattributes .gitignore; then echo Space at code block start found, aborting.; exit 1; fi
+
           - name: Set up Python
             uses: actions/setup-python@v4
             with: