Configure $SWH_SENTRY_DISABLE_LOGGING_EVENTS on loaders

swh-loader-core logs exceptions, then reports them to Sentry unless they are SystemExit/KeyboardInterrupt:

https://gitlab.softwareheritage.org/swh/devel/swh-loader-core/-/blob/741f874b4d9ee8bcb282a6ad318449361ac535ee/swh/loader/core/loader.py#L479-492

However, because $SWH_SENTRY_DISABLE_LOGGING_EVENTS is not true-ish, the exception log is captured by sentry:

• https://sentry.softwareheritage.org/share/issue/9ee5dc12934f42e888e51497d4e3c1c0/ (on loader-large-repository-* on prod)
• https://sentry.softwareheritage.org/share/issue/e4a28139397b4e14b9534bc8e9a6cde7/ (on loader-mercurial-* on staging)