fix(coverage): Disable certain coverage warnings.

These warnings appear if there are no Python source files in the
instrumented directories,
cf. #2762.

Work towards #2762

Author: phst

python/private/python_bootstrap_template.txt

@@ -438,6 +438,7 @@ def _RunForCoverage(python_program, main_filename, args, env,
   with open(rcfile_name, "w") as rcfile:
     rcfile.write('''[run]
 relative_files = True
+disable_warnings = module-not-imported, no-data-collected
 source =
 \t{source}
 '''.format(source=source))

python/private/stage2_bootstrap_template.py

@@ -321,6 +321,7 @@ def _maybe_collect_coverage(enable):
         rcfile.write(
             f"""[run]
 relative_files = True
+disable_warnings = module-not-imported, no-data-collected
 source =
 \t{source}
 """