include SRC_PATTERNS for ci_set_matrix

Originally, all Makefile variables were implicitly included in
settings[]. When I revised ci_set_matrix, only explicltly named
variables are included.

Depending on the set of changed files, ci_set_matrix needs the
SRC_PATTERNS variable, so include it explicitly.

Typical error, seen in the history of building this PR:
```
Traceback (most recent call last):
  File "/home/runner/work/circuitpython/circuitpython/tools/ci_set_matrix.py", line 309, in <module>
    main()
  File "/home/runner/work/circuitpython/circuitpython/tools/ci_set_matrix.py", line 305, in main
    set_boards(run_all)
  File "/home/runner/work/circuitpython/circuitpython/tools/ci_set_matrix.py", line 215, in set_boards
    if module in settings["SRC_PATTERNS"]:
                 ~~~~~~~~^^^^^^^^^^^^^^^^
KeyError: 'SRC_PATTERNS'
Error: Process completed with exit code 1.
```

Author: jepler

docs/shared_bindings_matrix.py

@@ -177,7 +177,7 @@ def get_settings_from_makefile(port_dir, board_name):
     in this script, something that has proved error-prone
     """
     contents = subprocess.run(
-        ["make", "-C", port_dir, "-f", "Makefile", f"BOARD={board_name}", "print-CFLAGS", "print-CIRCUITPY_BUILD_EXTENSIONS", "print-FROZEN_MPY_DIRS"],
+        ["make", "-C", port_dir, "-f", "Makefile", f"BOARD={board_name}", "print-CFLAGS", "print-CIRCUITPY_BUILD_EXTENSIONS", "print-FROZEN_MPY_DIRS", "print-SRC_PATTERNS"],
         encoding="utf-8",
         errors="replace",
         stdout=subprocess.PIPE,