chore: avoid deprecated funcs to calculate sha256

[federico-sysdig]

What type of PR is this?
/kind cleanup

Any specific area of the project related to this PR?
/area build

What this PR does / why we need it:
When building Falco with recent versions of OpenSSL all SHA256_* functions are reported as being deprecated. This PR uses a set of different functions to calculate a SHA256 checksum that avoids the deprecation. The behavior is the same.

Which issue(s) this PR fixes:
None

Special notes for your reviewer:

Does this PR introduce a user-facing change?:
No

NONE

[github-actions]

This PR may bring feature or behavior changes in the Falco engine and may require the engine version to be bumped.

Please double check userspace/engine/falco_engine_version.h file. See versioning for FALCO_ENGINE_VERSION.

/hold

[federico-sysdig]

/unhold

[FedeDP]

/approve

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: FedeDP, federico-sysdig

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[poiana]

LGTM label has been added.

Git tree hash: bea2aaab74499f092088b4e2bf3cee121b7ba1b7

[FedeDP]

/milestone 0.40.0

[federico-sysdig]

@incertum, may I ask you to double-check on this PR?
It's quick and I'd like to be sure that my desire to avoid functions that are deprecated in recent versions of OpenSSL is not causing disruption.

[poiana]

@Scutua: changing LGTM is restricted to collaborators

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[leogr]

Good catch! LGTM.

cc @LucaGuerra

/release-note-none

[FedeDP]

test-dev-packages-arm64

Isn't test-dev-packages-arm64 a required check?

[leogr]

test-dev-packages-arm64

Isn't test-dev-packages-arm64 a required check?

not sure about that 🤔 Maybe that is due to flaky arm tests? @LucaGuerra ?

[LucaGuerra]

Yes we had to disable that.