deps: pin urllib3>=2.6.0,<3 to match tableauserverclient

[jacalata]

Motivation

urllib3 was unpinned in tabcmd. pip resolved a compatible version
transitively through TSC, but the tabcmd distribution itself declared
no compatibility bounds. If TSC bumps its urllib3 range in a future
release, tabcmd installs could resolve to versions TSC was never tested
against.

Match TSC's declared pin directly so any Python environment installing
tabcmd resolves the same urllib3 range TSC uses in CI.

Behavior change

For users: none in practice; fresh install still resolves to
urllib3 2.6.3 today (same as before). Only the declared range changes.

The declared pin creates a duplicate source of truth with TSC. Long-term
solution is either drop this and rely on TSC's pin transitively, or
keep them in sync via a release checklist item.

Test plan

• No functional change; resolved urllib3 version unchanged on fresh
  install

🤖 Generated with Claude Code

[github-actions]

Coverage Report

File	Stmts	Miss	Cover	Missing
tabcmd
__main__.py	12	12	12	0%
_version.py	11	11	11	0%
tabcmd.py	15	15	15	0%
version.py	9	5	5	44%
tabcmd/commands
commands.py	10	10	10	0%
constants.py	77	18	18	77%
server.py	135	18	18	87%
tabcmd/commands/auth
session.py	394	50	50	87%
tabcmd/commands/datasources_and_workbooks
datasources_and_workbooks_command.py	157	18	18	89%
datasources_workbooks_views_url_parser.py	142	5	5	96%
delete_command.py	60	16	16	73%
export_command.py	120	25	25	79%
get_url_command.py	127	47	47	63%
publish_command.py	123	28	28	77%
runschedule_command.py	21	7	7	67%
tabcmd/commands/extracts
create_extracts_command.py	42	8	8	81%
decrypt_extracts_command.py	27	2	2	93%
delete_extracts_command.py	37	6	6	84%
encrypt_extracts_command.py	27	2	2	93%
extracts.py	20	2	2	90%
reencrypt_extracts_command.py	27	2	2	93%
refresh_extracts_command.py	48	10	10	79%
tabcmd/commands/group
create_group_command.py	29	5	5	83%
delete_group_command.py	27	2	2	93%
tabcmd/commands/project
create_project_command.py	46	8	8	83%
delete_project_command.py	35	4	4	89%
publish_samples_command.py	30	4	4	87%
tabcmd/commands/site
create_site_command.py	34	5	5	85%
delete_site_command.py	27	2	2	93%
edit_site_command.py	38	2	2	95%
list_command.py	77	12	12	84%
list_sites_command.py	29	2	2	93%
tabcmd/commands/user
add_users_command.py	29	5	5	83%
create_site_users.py	58	11	11	81%
create_users_command.py	59	9	9	85%
delete_site_users_command.py	43	5	5	88%
user_data.py	222	31	31	86%
tabcmd/execution
_version.py	2	2	2	0%
global_options.py	125	8	8	94%
localize.py	66	11	11	83%
logger_config.py	60	6	6	90%
tabcmd_controller.py	42	7	7	83%
TOTAL	2873	458	84%