Fix missing Qk prefix for C ExitCode (backport #14119)

[mergify]

Summary

Missed a Qk prefix for the ExitCode enum class, which should be called QkExitCode. This sort of problem will likely keep popping up since we're manually adding this prefix, until we get a solution like mozilla/cbindgen#1061.

---

This is an automatic backport of pull request #14119 done by [Mergify](https://mergify.com).

[qiskit-bot]

Thank you for opening a new pull request.

Before your PR can be merged it will first need to pass continuous integration tests and be reviewed. Sometimes the review process can be slow, so please be patient.

While you're waiting, please feel free to review other open PRs. While only a subset of people are authorized to approve pull requests for merging, everyone is encouraged to review open pull requests. Doing reviews helps reduce the burden on the core team and helps make the project's code better for everyone.

One or more of the following people are relevant to this code:

• @Qiskit/terra-core

[coveralls]

Pull Request Test Coverage Report for Build 14130016115

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 11 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.002%) to 88.082%

---

Files with Coverage Reduction	New Missed Lines	%
crates/qasm2/src/lex.rs	5	92.23%
crates/qasm2/src/parse.rs	6	97.61%

Totals
Change from base Build 14128040248:	-0.002%
Covered Lines:	72745
Relevant Lines:	82588

---

💛 - Coveralls