fix(deps): upgrade wagtail to 7.3.4 for security fixes

Resolves multiple high/medium severity Dependabot alerts covering
improper permission/restriction handling (Pages, translation, snippet
copy, Documents/Images API, image preview), document SHA1 disclosure,
reflected XSS in the dynamic image URL view, and a DoS via unbounded
filter specs.

GHSA-3vrh-m9w7-v94f, GHSA-jm5p-837g-rv8g, GHSA-x5cx-w6p2-mxf2,
GHSA-c2xx-cjmh-9q8f, GHSA-92hv-j533-69wc, GHSA-r6p4-grq7-xm4m,
GHSA-8634-mr4j-r72c, GHSA-f2p5-j6fg-5cxf, GHSA-23m2-mghx-vqmf,
GHSA-h54r-xq46-qwqm

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: matrixise

requirements/dev.txt

@@ -214,7 +214,7 @@ urllib3==2.7.0
     #   requests
 uv==0.11.19
     # via -r requirements/dev.in
-wagtail==7.3.2
+wagtail==7.3.4
     # via
     #   -c requirements/main.txt
     #   wagtail-factories

requirements/main.txt

@@ -181,7 +181,7 @@ urllib3==2.7.0
     # via
     #   botocore
     #   requests
-wagtail==7.3.2
+wagtail==7.3.4
     # via -r requirements/main.in
 whitenoise==6.12.0
     # via -r requirements/main.in