TT#44156 Support building against branch/{stretch,buster}/master

We usually use either "ignore" or "branch/master" and those are within
the 15 character limits of BuildTrunkDepForm() and
BuildTrunkReleaseForm().

But when building against "branch/stretch/master" or
"branch/buster/master", we trigger a `form validation error` because
both branch/stretch/master and branch/buster/master have more than 15
characters.

Raise character limit from 15 to 30 characters.

Change-Id: Icc1f8ee46dcb250c2d40da9ca25fef0d6924db1e

release_dashboard/forms/build.py

@@ -51,7 +51,7 @@ class BuildTrunkDepForm(BuildForm):
 
         for project in trunk_build_deps:
             self.fields['version_%s' %
-                        project] = forms.CharField(max_length=15)
+                        project] = forms.CharField(max_length=30)
 
 
 class BuildTrunkReleaseForm(BuildForm):
@@ -61,4 +61,4 @@ class BuildTrunkReleaseForm(BuildForm):
 
         for project in trunk_projects:
             self.fields['version_%s' %
-                        project] = forms.CharField(max_length=15)
+                        project] = forms.CharField(max_length=30)