Run each AppSec integration test in a separate process

[y9v]

What does this PR do?
This PR changes rake test:appsec:integration so that the task runs each test file as a separate process.

Motivation:
Rails has a lot of global state, which is quite hard to reset between tests that create different minimal Rails applications.

Change log entry
None. This change is internal.

Additional Notes:
None.

How to test the change?
CI

[datadog-datadog-prod-us1]

⚠️ Tests

⚠️ Warnings

❄️ 1 New flaky test detected

Rails Log Auto Injection with log injection enabled with Tagged Logging with Tagged logging setup and no tags injects trace_id into logs from rspec (Datadog) (✨ Fix with BitsAI)

server closed the connection unexpectedly
	This probably means the server terminated abnormally
	before or while processing the request.

Failure/Error: initialize!

PG::UnableToSend:
  server closed the connection unexpectedly
  	This probably means the server terminated abnormally
  	before or while processing the request.
...

ℹ️ Info

🧪 All tests passed

🎯 Code Coverage
• Patch Coverage: 100.00%
• Total Coverage: 101.99% (-0.01%)

View detailed report

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[pr-commenter]

Benchmarks

Benchmark execution time: 2025-10-02 12:36:45

Comparing candidate commit 05380dc in PR branch isolate-appsec-integration-tests with baseline commit 4ab26d0 in branch master.

Found 1 performance improvements and 0 performance regressions! Performance is the same for 43 metrics, 2 unstable metrics.

scenario:profiling - Allocations ()

• 🟩 throughput [+192197.257op/s; +200079.555op/s] or [+6.091%; +6.341%]

[y9v]

Closing this, since we have a ticket to work on that