chore(iast): fix header injection attr

[avara1986]

Fix validation introduced in #13546

APPSEC-57163

Checklist

• PR author has checked that all the criteria below are met
• The PR description includes an overview of the change
• The PR description articulates the motivation for the change
• The change includes tests OR the PR description describes a testing strategy
• The PR description notes risks associated with the change, if any
• Newly-added code is easy to change
• The change follows the library release note guidelines
• The change includes or references documentation updates if necessary
• Backport labels are set (if applicable)

Reviewer Checklist

• Reviewer has checked that all the criteria below are met
• Title is accurate
• All changes are related to the pull request's stated goal
• Avoids breaking API changes
• Testing strategy adequately addresses listed risks
• Newly-added code is easy to change
• Release note makes sense to a user of the library
• If necessary, author has acknowledged and discussed the performance implications of this PR as reported in the benchmarks PR comment
• Backport labels are set in a manner that is consistent with the release branch maintenance policy

[github-actions]

CODEOWNERS have been resolved as:

ddtrace/appsec/_iast/_logs.py                                           @DataDog/asm-python
ddtrace/appsec/_iast/taint_sinks/header_injection.py                    @DataDog/asm-python

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-06-09 08:06:01

Comparing candidate commit f9a090d in PR branch avara1986/fix_header_value with baseline commit 10e09e0 in branch main.

Found 0 performance improvements and 5 performance regressions! Performance is the same for 552 metrics, 7 unstable metrics.

scenario:iastaspects-lower_aspect

• 🟥 execution_time [+208.354ns; +259.404ns] or [+9.251%; +11.517%]

scenario:iastaspects-replace_aspect

• 🟥 execution_time [+398.692ns; +528.493ns] or [+8.477%; +11.237%]

scenario:iastaspects-upper_aspect

• 🟥 execution_time [+237.893ns; +270.746ns] or [+10.614%; +12.080%]

scenario:iastaspectsospath-ospathnormcase_aspect

• 🟥 execution_time [+363.754ns; +435.539ns] or [+10.467%; +12.533%]

scenario:iastaspectsospath-ospathsplit_aspect

• 🟥 execution_time [+767.358ns; +895.131ns] or [+15.891%; +18.537%]

[github-actions]

Bootstrap import analysis

Comparison of import times between this PR and base.

Summary

The average import time from this PR is: 280 ± 4 ms.

The average import time from base is: 280 ± 4 ms.

The import time difference between this PR and base is: -0.4 ± 0.2 ms.

The difference is not statistically significant (z = -2.34).

Import time breakdown

The following import paths have shrunk:

ddtrace.auto 1.271 ms (0.45%)

ddtrace 0.670 ms (0.24%)

ddtrace.internal._unpatched 0.022 ms (0.01%)

ddtrace.bootstrap.sitecustomize 0.601 ms (0.21%)

ddtrace.bootstrap.preload 0.601 ms (0.21%)

ddtrace.internal.remoteconfig.client 0.601 ms (0.21%)