bump `nim-confutils` to `6c3566850d5ec241d8cb687ae8461c972040311a` (#5046)

- remove support for Nim v1.2 and v1.4
- use --mm: instead of --gc: and remove stddefects import
- annotate `parseCmdArg` with `{.raises.}`
- ignore exceptions while writing to stdout/stderr
- handle `terminalWidth` exception
- catch exceptions in `appInvocation`

vendor/nim-confutils

@@ -1 +1 @@
-Subproject commit 2028b41602b3abf7c9bf450744efde7b296707a2
+Subproject commit 6c3566850d5ec241d8cb687ae8461c972040311a