Fix indent warning

[gassmoeller]

Running the indent script used to produce the following warning for a while now:

xargs: warning: options --max-args and --replace/-I/-i are mutually exclusive, ignoring previous --max-args value

This PR fixes the warning by removing the -n (max-args) option that was ignored anyway. It also takes over some improvements from geodynamics/aspect#6153 to print file names separated by NULL characters to avoid problems with spaces and special characters in file names.

[MFraters]

Thanks!

[github-actions]

Benchmark	Main	Feature	Difference (99.9% CI)
Slab interpolation simple none	1.119 ± 0.010 (s=389)	1.117 ± 0.009 (s=419)	-0.4% .. +0.0%
Slab interpolation curved simple none	1.122 ± 0.013 (s=411)	1.120 ± 0.012 (s=394)	-0.4% .. +0.1%
Spherical slab interpolation simple none	1.105 ± 0.009 (s=406)	1.105 ± 0.011 (s=411)	-0.2% .. +0.2%
Slab interpolation simple curved CMS	1.164 ± 0.010 (s=384)	1.169 ± 0.012 (s=390)	+0.2% .. +0.6%
Spherical slab interpolation simple CMS	1.450 ± 0.012 (s=307)	1.453 ± 0.013 (s=315)	+0.0% .. +0.5%
Spherical fault interpolation simple none	1.102 ± 0.010 (s=402)	1.101 ± 0.009 (s=417)	-0.3% .. +0.1%
Cartesian min max surface	2.546 ± 0.020 (s=151)	2.546 ± 0.021 (s=205)	-0.3% .. +0.3%
Spherical min max surface	7.174 ± 0.079 (s=70)	7.172 ± 0.077 (s=58)	-0.7% .. +0.6%