List-fields for source and target are too small in "new pull request" wizard

[Frickeldave]

• Gitea version (or commit ref): 1.13.6
• Git version: Latest
• Operating system: Debian 9 and Debian 10
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No

Description

When you have multiple branches with a very long organisation name, it is impossible to identify the "correct" target or source branch in the drop-down lists, when you create a new pull request. It should be great, if you use the complete available space of the control.

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Screenshots