Fix CLI ERC tests failing due to hardcoded KICAD9 env vars

The CLI test harness hardcoded KICAD9_SYMBOL_DIR and KICAD9_FOOTPRINT_DIR,
which stopped working after the version bump to KiCad 10. The versioned
env var fallback in KIwxExpandEnvVars could no longer resolve
KICAD8_FOOTPRINT_DIR references in fp-lib-table because the predefined
list only contains KICAD10_FOOTPRINT_DIR.

Dynamically detect the major version from kicad-cli at test startup and
set the matching versioned env vars. Also fix a pre-existing TypeError
when QA_DATA_ROOT is set (str vs Path).

Set footprint_link_issues to ignore in the test project to eliminate
environment-dependent ERC output, and update all three golden files
with the new ignored check entry.

qa/data/cli/basic_test/basic_test.erc.json

@@ -11,6 +11,10 @@
             "description": "Four connection points are joined together",
             "key": "four_way_junction"
         },
+        {
+            "description": "Footprint link issue",
+            "key": "footprint_link_issues"
+        },
         {
             "description": "Assigned footprint doesn't match footprint filters",
             "key": "footprint_filter"