regen_headers: pass --no-validate to mavgen.py

We don't care about XSD strictness for this build path — older
pymavlink installs reject newer XML elements (e.g. <superseded>)
and abort header generation before any C is emitted. --no-validate
skips the schema check while still parsing/generating fine. Avoids
the schema-version drift biting deploys to servers with older
pymavlinks.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: tridge

regen_headers.sh

@@ -3,7 +3,7 @@
 
 echo "Generating mavlink2 headers"
 rm -rf libraries/mavlink2/generated
-mavgen.py --wire-protocol 2.0 --lang C modules/mavlink/message_definitions/v1.0/all.xml -o libraries/mavlink2/generated
+mavgen.py --no-validate --wire-protocol 2.0 --lang C modules/mavlink/message_definitions/v1.0/all.xml -o libraries/mavlink2/generated
 
 ./git-version.sh