unit-test: add meson version check for get_variable

Some repositories are using the newer `get_variable` call in meson
without a keyword argument.  This requires meson 0.58 or later.  I've
contributed fixes for all repositories under the
`meson_deprecated_pkgconfig` topic and so am also adding a CI catch
to prevent future regressions.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I9465c3946825ec96d0c934635685e85d74fdf4ee
diff --git a/scripts/unit-test.py b/scripts/unit-test.py
index 0bf45a0..21b7022 100755
--- a/scripts/unit-test.py
+++ b/scripts/unit-test.py
@@ -1110,6 +1110,15 @@
                     + "meson_version: '>=0.57'"
                 )
 
+        if "get_variable(" in build_contents:
+            if not meson_version or not meson_version_compare(
+                meson_version, ">=0.58"
+            ):
+                raise Exception(
+                    "dep.get_variable() with positional argument requires "
+                    + "meson_Version: '>=0.58'"
+                )
+
 
 class Package(object):
     def __init__(self, name=None, path=None):