gdb: re-format with black 21.9b0

Run black 21.9b0 on gdb/ (this is the version currently mentioned on the
wiki [1], the subsequent commit will bump that version).

[1] https://sourceware.org/gdb/wiki/Internals%20GDB-Python-Coding-Standards

Change-Id: I5ceaab42c42428e053e2572df172aa42a88f0f86
3 files changed