fix: allow parsing of github expressions containing non-breaking-space characters, and allow dataflow analysis to fail

[nicallen]

…to analyse a workflow without crashing Macaron entirely.

Summary

Fixes a crash caused by github expression parser not handling non-breaking-space characters (encountered when analysing https://github.com/openjdk/lanai and https://github.com/openjdk/jdk17u-ri).
Also allows Macaron to continue even if dataflow analysis fails (in which case only analysis of the offending workflow is skipped), which is useful to mitigate the impact of analysis bugs, as well as gracefully handle cases where a workflow is genuinely malformed (e.g. in one of the workflows of pkg:pypi/jupyter-client@8.7.0).
Also improves error reporting when the dataflow analysis fails, to report the failing workflow file.

Description of changes

Related issues

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