tests: Search the appropriate directories for our GIR XML inputs

During "as-installed" testing, we should search the GIR_DIR for GIR XML,
instead of hard-coding that it is `${prefix}/share/gir-1.0`. This is
not the case on at least Debian, in order to make it possible to
install more than one architecture's flavour of `GLib-2.0.gir`,
which contains some architecture-specific `#define`s.

Also search GOBJECT_INTROSPECTION_DATADIR/GIR_SUFFIX (in practice
something like `/usr/share/gir-1.0` in all cases) to accommodate
distributions like Debian that move the architecture-independent
majority of GIR XML into /usr/share to avoid duplication, leaving
only the architecture-specific minority of files like `GLib-2.0.gir`
in the GIR_DIR.

Signed-off-by: Simon McVittie <smcv@collabora.com>

tests/flake8.sh

@@ -21,7 +21,7 @@ run_lint () {
     # shellcheck disable=SC2046
     flake8 \
         --max-line-length=88 --ignore="$formatting_warnings" \
-        $(git ls-files '*.py')
+        $(git ls-files '*.py' 'tests/lib/*.py.in')
 }
 
 # shellcheck source=tests/lint-common.sh