Skip line if no match against inventory line regex

[jb3]

We currently have an issue on bot (BOT-3VH on Sentry) which is failing to parse the sympy docs due to a malformed object inventory.

This looks to be caused by multi-line figure descriptions or something similar which are creating lines that do not match our regex.

Ignoring these lines is fine as they likely provide no additional context anyway, and the relevant symbol is still parsed as normal and links to the original docs.

[sentry-io[bot]]

Sentry Issue: BOT-3VH

[ChrisLovering]

/merge