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What does this MR do?

Upgrade the vendored Git Submodules to more recent versions. Both libraries have not had any breaking API changes recently, so upgrading should be rather smooth and there is no real need for sticking to a particular (release) version.

• Update spdlog to latest version of branch v1.x.
• Update googletest to latest version of branch master.

Is there something that needs to be double checked?

No.

Can this MR be accepted?

• Updated submodules
• Added/Updated documentation
• Pipeline passing
• Squash option set
• Delete branch option set
• Added entry to CHANGELOG.md

Assignee: If the Squash option is set, check/update the commit message right before merging!

Related issues

Closes #184 (closed)