Update GCC 10.x to 11.x in CI tests

[mlxd]

Issue description

Lightning currently builds on Ubuntu 22.04 and GCC 10 for all tests. We can update the compiler to instead use GCC 11 for all tests under Linux.

• Update all references from gcc-10 to gcc-11 in https://github.com/PennyLaneAI/pennylane-lightning/blob/master/.github/workflows/tests_linux.yml
• Update all references from g++-10 to g++-11 in https://github.com/PennyLaneAI/pennylane-lightning/blob/master/.github/workflows/tests_linux.yml
• Ensure CI tests pass as expected.

[mlxd]

Closed by #370