fix: use a raw string for EMAIL_CATCH_ALL_PATTERN

[pando85]

Problem

image_root/scripts/email-anonymizer.py:37 builds the catch-all pattern from a normal string
literal containing \[, \. and \{. None of those are valid Python escape sequences — they
survive only because Python leaves unknown escapes as-is.

Python 3.12 promoted that from a DeprecationWarning to a visible SyntaxWarning, and since
v5.0.0 moved the image to Debian Trixie (Python 3.13) it now shows up at runtime:

SyntaxWarning: "\[" is an invalid escape sequence. Such sequences will not work in the future.
Did you mean "\\["? A raw string is also an option.

It is more than cosmetic noise. With ANONYMIZE_EMAILS set, rsyslog runs this script via
mmexternal and reads its replies over a pipe, so the warning lands on that channel and rsyslog
rejects it as a bad reply:

rsyslogd: mmexternal: invalid reply '/scripts/email-anonymizer.py:37: SyntaxWarning: invalid
escape sequence '\['   EMAIL_CATCH_ALL_PATTERN = ...' from program '/scripts/email-anonymizer.sh'

This happens once per anonymizer process start — and again whenever the wrapper's
while ! ... ; do sleep 1; done retry loop restarts it. The log message being processed at that
moment doesn't get anonymized.

Fix

Make the literal a raw string.

One thing worth flagging for review: just adding the r prefix would silently change the
pattern. The literal already contains \\[ and \\] in the first character class, which in a
raw string would mean a literal backslash followed by [ — altering what the class matches. So
the pre-escaped sequences are collapsed in the same change (\\[ → \[, \\] → \],
\\{ → \{), which leaves the compiled pattern byte-for-byte identical to before.

Verification

• The resulting pattern string is unchanged (compared repr() of the literal before and after).
• The SyntaxWarning is gone; no other warnings appear.
• The input vectors from unit-tests/024_email-anonymizer-smart.bats and
  unit-tests/025_email-anonymizer-regexs.bats produce identical output before and after,
  across the noop, hash, paranoid and smart filters — 190 input × filter comparisons,
  zero differences. 025's own expectations still pass unchanged.

[bokysan]

Nice catch! Thank you for the fix!