test: resolve bugs in sourcecode analyzer to allow unit tests to run offline

[art1f1c3R]

Summary

To address #1129, this PR modifies some configurations for Semgrep in pypi_sourcecode_analyzer to allow unit tests to run completely offline.

Description of changes

The following command line arguments are added to prevent operations in Semgrep that make network connections:

• Semgrep metrics are disabled, as these make network connections to metrics.semgrep.dev:443.
• The version check is disabled, as this makes a connection to Semgrep servers to see if the latest version is run.

After adding this, there are still network connections made by semgrep scan --validate to pull in linting rules. Currently, there is no way to run this without pulling in the rules using that remote connection (a feature request for this is here). To allow this functionality to still exist, instead of raising a ConfigurationError at initialisation, instead it logs a warning if the validation process failed, so if it failed due to being unable to make a network connection, it can still continue. The error is then cause in the analyze function when trying to run Semgrep. Changing this to a warning and not an error will not have an effect on any existing functionality.

Related issues

Closes #1129.

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