gh-107450: Fix testMemoryErrorBigSource in test_exceptions

[serhiy-storchaka]

1. It uses 4GB of memory, not 3GB.
2. It should be skipped if not enough memory
3. Scope is too wide: the error may occur not only at compile time, but may also occur when the source line is generated or when the compiled code is executed.

• Issue: string length overflows to negative when executing #107450

[serhiy-storchaka]

This PR also slightly optimizes the test: now it is 7 seconds faster on my computer (23 seconds instead of 30 seconds).

[lysnikolaou]

@serhiy-storchaka I've opened #110832 that fixes the test. Maybe push the optimization to that branch?

[serhiy-storchaka]

Included in #110832.