GH-49380: [R] Add missing Ubuntu reinstall step in setup.Rmd to fix r-devdocs ABI mismatch

Author: vanshaj2023

r/vignettes/developers/setup.Rmd

@@ -354,6 +354,10 @@ sudo apt install -y -V libarrow-dev
 MAKEFLAGS="LDFLAGS=" R CMD INSTALL .
 ```
 
+```{bash, save=run & !sys_install & ubuntu}
+MAKEFLAGS="LDFLAGS=" R CMD INSTALL .
+```
+
 ## `rpath` issues
 
 If the package fails to install/load with an error like this: