Fix events and workflow_runs datetimes in source-github

[evantahler]

closes #19298

[evantahler]

/test connector=connectors/source-github

🕑 connectors/source-github https://github.com/airbytehq/airbyte/actions/runs/3439637683
✅ connectors/source-github https://github.com/airbytehq/airbyte/actions/runs/3439637683
Python tests coverage:

Name                             Stmts   Miss  Cover
----------------------------------------------------
source_github/utils.py              14      0   100%
source_github/github_schema.py    8807      0   100%
source_github/__init__.py            2      0   100%
source_github/graphql.py           145      1    99%
source_github/streams.py           796     44    94%
source_github/source.py            104     27    74%
----------------------------------------------------
TOTAL                             9868     72    99%
	 Name                                                 Stmts   Miss  Cover   Missing
	 ----------------------------------------------------------------------------------
	 source_acceptance_test/base.py                          12      4    67%   16-19
	 source_acceptance_test/config.py                       139      5    96%   87, 93, 235, 239-240
	 source_acceptance_test/conftest.py                     196     92    53%   35, 41-43, 48, 54, 60, 66, 72-74, 93, 98-100, 106-108, 114-115, 120-121, 126, 132, 141-150, 156-161, 176, 200, 231, 237, 243-248, 256-261, 269-282, 287-293, 300-311, 318-334
	 source_acceptance_test/plugin.py                        69     25    64%   22-23, 31, 36, 120-140, 144-148
	 source_acceptance_test/tests/test_core.py              353    110    69%   53, 64-72, 77-84, 88-89, 93-94, 192, 230-247, 256-264, 268-273, 279, 312-317, 355-362, 405-407, 410, 475-483, 495-498, 503, 559-560, 566, 569, 605-615, 628-653
	 source_acceptance_test/tests/test_incremental.py       158     14    91%   52-59, 64-77, 240
	 source_acceptance_test/utils/asserts.py                 37      2    95%   57-58
	 source_acceptance_test/utils/common.py                  94     10    89%   16-17, 32-38, 72, 75
	 source_acceptance_test/utils/compare.py                 62     23    63%   21-51, 68, 97-99
	 source_acceptance_test/utils/connector_runner.py       112     50    55%   23-26, 32, 36, 39-68, 71-73, 76-78, 81-83, 86-88, 91-93, 96-114, 148-150
	 source_acceptance_test/utils/json_schema_helper.py     105     13    88%   30-31, 38, 41, 65-68, 96, 120, 190-192
	 ----------------------------------------------------------------------------------
	 TOTAL                                                 1516    348    77%

Build Passed

Test summary info:

All Passed

[evantahler]

/publish connector=connectors/source-github

🕑 Publishing the following connectors:
connectors/source-github
https://github.com/airbytehq/airbyte/actions/runs/3439929123

Connector	Did it publish?	Were definitions generated?
connectors/source-github	✅	✅

if you have connectors that successfully published but failed definition generation, follow step 4 here ▶️