main/doxygen: temporarily allow textrels on riscv64

On riscv64 builder it stuck with

Install the project...
-- Install configuration: "None"
-- Installing: /home/buildozer/aports/main/doxygen/pkg/doxygen/usr/bin/doxygen
make: Leaving directory '/home/buildozer/aports/main/doxygen/src/doxygen-1.9.2/build'
>>> doxygen*: Running postcheck for doxygen
>>> ERROR: doxygen*: Found textrels:
TEXTREL  /home/buildozer/aports/main/doxygen/pkg/doxygen/usr/bin/doxygen
>>> ERROR: doxygen*: prepare_subpackages failed
>>> ERROR: doxygen: rootpkg failed