Fix warnings when using typst 0.12.0 (#71)

* fixes for warnings with typst 0.12.0
* update tests for typst 0.12.0
* update github test workflow for typst 0.12
* chore: apply typst updates to test code
* chore: update compiler version in typst.toml
* chore: use the correct preview version in coverletter2
* chore: improve comments in coverletter template
* chore: update test references
* fix: issues with coverletter for typst `0.12.0`
* update test references with typst-test update

---------

Co-authored-by: Paul Tsouchlos <developer.paul.123@gmail.com>

.github/workflows/tests.yml

@@ -10,11 +10,11 @@ jobs:
     strategy:
       matrix:
         # add any other Typst versions that your package should support
-        typst-version: ["0.11"]
+        typst-version: ["0.12"]
         # the docs don't need to build with all versions supported by the package;
         # the latest one is enough
         include:
-          - typst-version: "0.11"
+          - typst-version: "0.12"
             doc: 1
     runs-on: ubuntu-latest
     steps: