Cannot use variables for Z parameter in G1 command

[RevoAlex]

I just noticed that I cannot use local and global variables for the Z parameter in G1 commands. It only happens for the Z parameter. X, Y and E (even with multi extruder) are working just fine. Unfortunately I cannot update the Duet currently because it's heavily used but I could not find any bug fixes in the changelogs.

Steps to reproduce

1. Have a Duet MB6HC in SBC mode with version 3.5.1.
2. Create .gcode or .g file in jobs with this content:

var test = 1
G1 Z{var.test}

3. Open the job file list.

Expected behavior

Correct parsing of Gcode file.

Actual behavior

Error message with:

Failed to get file info for test.gcode
Cannot convert Z parameter to Single (value {var.test})

[dc42]

@RevoAlex please upgrade to 3.5.4 and test again.