tests: look for sRGB.icc in several paths, skip related tests if not found

This is no longer the case with ImageMagick 7.

src/img2pdf_test.py

@@ -21,7 +21,17 @@ import json
 import pathlib
 
 SCRIPT_DIR = pathlib.Path(__file__).resolve().parent
-ICC_PROFILE = SCRIPT_DIR / "tests" / "data" / "sRGB.icc"
+ICC_PROFILE = None
+ICC_PROFILE_PATHS = (
+        "/usr/share/color/icc/ghostscript/srgb.icc",
+        "/usr/share/ghostscript/9.54.0/iccprofiles/srgb.icc",
+        "/usr/share/color/icc/sRGB.icc",
+        "/usr/share/color/icc/OpenICC/sRGB.icc",
+)
+for path in ICC_PROFILE_PATHS:
+    if os.path.exists(path):
+        ICC_PROFILE = path
+        break
 
 HAVE_MUTOOL = True
 try:
@@ -307,6 +317,8 @@ def compare(im1, im2, exact, icc, cmyk):
     else:
         iccargs = []
         if icc:
+            if ICC_PROFILE is None:
+                pytest.skip("Could not locate an ICC profile")
             iccargs = ["-profile", ICC_PROFILE]
         psnr = subprocess.run(
             ["compare"]
@@ -420,6 +432,8 @@ def compare_pdfimages_png(tmpdir, img, pdf, exact=True, icc=False):
         )
     else:
         if icc:
+            if ICC_PROFILE is None:
+                pytest.skip("Could not locate an ICC profile")
             psnr = subprocess.run(
                 [
                     "compare",