fix: update PyYAML, Cython to resolve Docker build

An issue with the PyYAML library causes the container used to run
Taskcat to fail when installing taskcat using pip. This seems to be
caused by a regression introduced in Cython 3.0.0a10.

The issue was identified and resolved by @cormac-yobota and this commit
implements the fix proposed in issue #350.

For more details, see:
- https://bit.ly/3Ayigfi for the issue opened by @cormac-yobota
  describing the problem and the fix in the action-taskcat repository

- https://bit.ly/3CyCCW8 for the issue opened against the PyYAML project,
  describing the regression introduced in Cython 3.0.0a10

Co-authored-by: Cormac Murphy <cormac@yobota.xyz>
Associated issue: #350

Dockerfile

@@ -2,7 +2,9 @@ FROM python:3.8.13-alpine3.15
 
 RUN apk add --no-cache python3-dev~3.9 gcc~10 libc-dev~0.7 nodejs~16 npm~8 && rm -rf /var/cache/apk/*
 
-RUN pip3 install taskcat==0.9.23 --upgrade
+RUN pip3 install --upgrade pip && \
+    pip3 install "Cython<3.0" "pyyaml<6" --no-build-isolation && \
+    pip3 install taskcat==0.9.23 --upgrade
 
 COPY entrypoint.sh /entrypoint.sh
 RUN chmod +x /entrypoint.sh