Fix crashtracking tests

[kevingosse]

Motivation

is_crash_report doesn't behave correctly when it receives telemetry logs that are not a crash report.

Changes

Assertions were added in #3080. Instead, the is_crash_report function should just return false.

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[cbeauchesne]

Assertions were added in #3080

More precisely : Before #3080 , the function raised an exception hard to understand when the data was not on the expected format. The PR didn't add any particular check, but juste made the exception easier to understand 😉