ci: move lychee's .lycheeignore exclusion into the hook

The "--exclude-path .lycheeignore" arg looked redundant, since lychee
reads the URL patterns from that file on its own.  It was not: the arg
also kept the file out of the *inputs*, and pre-commit hands the hook
every changed file - so on a push touching .lycheeignore, lychee read
it as plain text, pulled 26 junk URLs out of the regexes
("https://posteo/" and friends) and failed.  The arg is dropped and
the file is excluded through pre-commit's own "exclude" instead.

Prompt: drop the noop-thing from .pre-commit-config.yaml [the
"--exclude-path .lycheeignore" arg, which I had wrongly called a no-op]

Assisted-By: Claude Opus 5 <noreply@anthropic.com>

Author: tobixen

.pre-commit-config.yaml

@@ -35,6 +35,10 @@ repos:
     rev: lychee-v0.24.2
     hooks:
       - id: lychee
-        args: ["--no-progress", "--timeout", "10", "--exclude-path", ".lycheeignore", "--max-cache-age=30d", "--cache"]
+        args: ["--no-progress", "--timeout", "10", "--max-cache-age=30d", "--cache"]
         stages: [pre-push]
-        exclude: ^tests/test_caldav_unit\.py$
+        ## lychee reads the URL patterns from .lycheeignore by itself.  The
+        ## dropped "--exclude-path .lycheeignore" arg did something else: it
+        ## kept that file out of the *inputs*, which is needed, as lychee
+        ## otherwise reads it as text and extracts junk URLs from the regexes.
+        exclude: ^(tests/test_caldav_unit\.py|\.lycheeignore)$