.github: dependabot: Fix the 'exclude_patterns' config typo

s/exclude_patterns/exclude-patterns [1].

Since an official native validation solution doesn't exist yet [2] that
would work reliably, @bugron/validate-dependabot-yaml was used to
validate this typo fix.

[1] https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/configuration-options-for-the-dependabot.yml-file#groups
[2] dependabot/dependabot-core#4605
[3] https://www.npmjs.com/package/@bugron/validate-dependabot-yaml

Signed-off-by: Erik Skultety <eskultet@redhat.com>

.github/dependabot.yml

@@ -24,7 +24,7 @@ updates:
         update-types:
           - "minor"
           - "patch"
-        exclude_patterns:
+        exclude-patterns:
           - "pydantic*"
 
       # pydantic is a known violator of version updates where they don't release the core backend