Add ERT explainer for 'tramp--test-file-attributes-equal-p'

* test/lisp/net/tramp-tests.el (tramp--test-file-attributes-equal-p):
Use ERT explainer for 'equal' to improve failure messages.
1 job for master in 53 minutes and 16 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
failed #1403
test-all

00:53:16

 
Name Stage Failure
failed
test-all Test
Makefile:313: recipe for target 'check-doit' failed
make[2]: *** [check-doit] Error 1
make[2]: Leaving directory '/builds/emacs/emacs/test'
Makefile:288: recipe for target 'check-expensive' failed
make[1]: *** [check-expensive] Error 2
make[1]: Leaving directory '/builds/emacs/emacs/test'
Makefile:962: recipe for target 'check-expensive' failed
make: *** [check-expensive] Error 2
ERROR: Job failed: exit code 1