Left-axis-format doesn't allow me to print SI units

[mpikzink]

Describe the bug
The regexp check in --left-axis-format doesn't allow to print SI units like kWh or in that case krpm

%5.1lf%Srpm

while GPRINT:sensor:MIN:%5.1lf%Srpm does work like I expect.

To Reproduce
RRDTool Command

rrdtool graph /tmp/wQnE1vf6MRRW4HkB --start 1731938400 --end 1732025700 --width 1707 --height 988 --imgformat=SVG --font LEGEND:8:DejaVuSansMono --font AXIS:7:DejaVuSansMono --font-render-mode normal -c FONT\#000000 -c BACK\#EEEEEE00 -c SHADEA\#EEEEEE00 -c SHADEB\#EEEEEE00 -c CANVAS\#FFFFFF00 -c GRID\#a5a5a5 -c MGRID\#FF9999 -c FRAME\#5e5e5e -c ARROW\#5e5e5e --alt-autoscale-max --rigid --slope-mode  --vertical-label "Fanspeed" --left-axis-format "%5.1lF%Srpm" DEF:sensor=xxx/sensor-fanspeed-ipmi-Fan1A.rrd:sensor:AVERAGE DEF:sensor_max=xxx/sensor-fanspeed-ipmi-Fan1A.rrd:sensor:MAX DEF:sensor_min=xxx/sensor-fanspeed-ipmi-Fan1A.rrd:sensor:MIN AREA:sensor_max\#c5c5c5 AREA:sensor_min\#ffffffff COMMENT:"Alert tresholds\\:" LINE1.5:600\#00008b:"low = 600rpm":dashes LINE1.5:960\#005bdf:"warn low = 960rpm":dashes COMMENT:"\\n" COMMENT:"                               Now      Avg     Min     Max\\n" LINE2:sensor\#000000:"Fan1A                     " GPRINT:sensor:LAST:%5.1lf%Srpm GPRINT:sensor:AVERAGE:%5.1lf%Srpm GPRINT:sensor:MIN:%5.1lf%Srpm GPRINT:sensor:MAX:%5.1lf%Srpm\\l --daemon unix:/var/run/rrdcached.sock

RRDTool Output

ERROR: invalid format string '%5.1lF%Srpm' (should match '^(?:[^%]+|%%)*%[-+ 0#]?[0-9]*(?:[.][0-9]+)?l[eEfFgG](?:[^%]+|%%)*$')

Expected behavior
A clear and concise description of what you expected to happen.

Screenshots
I like to see the SI units also in the Y-Axis

Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Tested with RRDTool 1.7.2
The GPRINT %S issue was part of the release notes there