allplatformstests: use subTests with test_warning_location

unittests/allplatformstests.py

@@ -1932,6 +1932,7 @@ class AllPlatformTests(BasePlatformTests):
             r'meson.build:7: WARNING: Module unstable-simd has no backwards or forwards compatibility and might not exist in future releases.',
             r"meson.build:11: WARNING: The variable(s) 'MISSING' in the input file 'conf.in' are not present in the given configuration data.",
         ]:
+            with self.subTest(expected):
                 self.assertRegex(out, re.escape(expected))
 
         for wd in [
@@ -1939,6 +1940,7 @@ class AllPlatformTests(BasePlatformTests):
             self.builddir,
             os.getcwd(),
         ]:
+            with self.subTest(wd):
                 self.new_builddir()
                 out = self.init(tdir, workdir=wd)
                 expected = os.path.join(relpath(tdir, self.src_root), 'meson.build')