add os.getenv to the support matrix

Author: jepler

docs/shared_bindings_matrix.py

@@ -72,6 +72,7 @@
     "collections": "CIRCUITPY_COLLECTIONS",
     "fontio": "CIRCUITPY_DISPLAYIO",
     "io": "CIRCUITPY_IO",
+    "os.getenv": "CIRCUITPY_OS_GETENV",
     "select": "MICROPY_PY_USELECT_SELECT",
     "sys": "CIRCUITPY_SYS",
     "terminalio": "CIRCUITPY_DISPLAYIO",
@@ -86,6 +87,7 @@
     "collections",
     "errno",
     "json",
+    "os.getenv",
     "re",
     "select",
     "sys",