[tests] Allow arbitrary build directories.

* tests/issue-1063/main.c (main): I am building with a build
directory that is not directly inside the source tree, so the path
`../tests/data/As.I.Lay.Dying.ttf` does not resolve to the test
input file.  This change passes the test data directory as an
environment variable to allow arbitrary build directories.

* tests/meson.build: Updated.
3 files changed