Fix #2317, Correct unbalanced brackets in CFE_MSG_CMD_HDR_INIT macro

[thnkslprpt]

Checklist

• I reviewed the Contributing Guide.
• I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution

• Fixes wrong closing parenthesis in CFE_MSG_CMD_HDR_INIT macro #2317
  • unbalanced brackets/parentheses corrected

Testing performed
GitHub CI actions all passing successfully.

Expected behavior changes
Balanced brackets - could avoid future compiler warnings/errors or code bugs if not picked up by the compiler.

Contributor Info
Avi Weiss @thnkslprpt

[skliper]

Ouch. Slightly related:

• Add functional tests for cFE Message extended header APIs  #1810

Recommend adding tests that use this in CI.