tests: Add $(srcdir) to Perl's module search path.

Dependencies

• [2] HX4QYOYA add first evaluations tests
• [3] HHPQFVQM add local srcdir to perl5lib env var
• [4] WHS5RMPO
• [*] G2ZB6464 first test, not yet in buildprocess

Change contents

• replacement in tests/Makefile.am at line 10
  [2.381]→[3.0:46](∅→∅),[3.291]→[3.0:46](∅→∅)
  − PERL5LIB=$$PERL5LIB:$(top_srcdir)/src/lib \
  [2.381]

  [3.291]
  + PERL5LIB="$(srcdir):$(top_srcdir)/src/lib:$$PERL5LIB" \