Change base class of TimeZoneSerializerField from DJRF's Field to CharField #380

Job	Run time
Lint	31s
Test py3.8, dj4.2, pytz, sqlite	47s
Build	22s
Test py3.8, dj4.2, zoneinfo, sqlite	50s
Test py3.8, dj4.2, pytz, postgres	47s
Test py3.8, dj4.2, zoneinfo, postgres	47s
Test py3.9, dj4.2, pytz, sqlite	50s
Test py3.9, dj4.2, zoneinfo, sqlite	1m 1s
Test py3.9, dj4.2, pytz, postgres	50s
Test py3.9, dj4.2, zoneinfo, postgres	52s
Test py3.10, dj4.2, pytz, sqlite	47s
Test py3.10, dj4.2, zoneinfo, sqlite	49s
Test py3.10, dj4.2, pytz, postgres	52s
Test py3.10, dj4.2, zoneinfo, postgres	55s
Test py3.10, dj5.0, zoneinfo, sqlite	1m 1s
Test py3.10, dj5.0, zoneinfo, postgres	53s
Test py3.10, dj5.1b1, zoneinfo, sqlite	55s
Test py3.10, dj5.1b1, zoneinfo, postgres	57s
Test py3.11, dj4.2, pytz, sqlite	57s
Test py3.11, dj4.2, zoneinfo, sqlite	48s
Test py3.11, dj4.2, pytz, postgres	50s
Test py3.11, dj4.2, zoneinfo, postgres	53s
Test py3.11, dj5.0, zoneinfo, sqlite	47s
Test py3.11, dj5.0, zoneinfo, postgres	54s
Test py3.11, dj5.1b1, zoneinfo, sqlite	48s
Test py3.11, dj5.1b1, zoneinfo, postgres	51s
Test py3.12, dj4.2, pytz, sqlite	56s
Test py3.12, dj4.2, zoneinfo, sqlite	53s
Test py3.12, dj4.2, pytz, postgres	56s
Test py3.12, dj4.2, zoneinfo, postgres	1m 2s
Test py3.12, dj5.0, zoneinfo, sqlite	54s
Test py3.12, dj5.0, zoneinfo, postgres	1m 0s
Test py3.12, dj5.1b1, zoneinfo, sqlite	51s
Test py3.12, dj5.1b1, zoneinfo, postgres	1m 0s
	29m 6s

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