Fix Arkansas capital gain loss cap parameter values

[martinholmer]

The 2021 AR1000D form says this in RED:

.
.

But the following loss_cap.yaml file has different values:

policyengine-us/policyengine_us/parameters/gov/states/ar/tax/income/gross_income/capital_gains/loss_cap.yaml

Lines 1 to 29 in c64a7a2

	description: Arkansas taxes the capital gain loss up to this amount, based on filing status.
	metadata:
	unit: currency-USD
	period: year
	breakdown:
	- filing_status
	label: Arkansas long-term capital gains tax loss cap
	reference:
	# The loss threshold is not defined in the legal code
	- title: Arkansas Code Title 26. Taxation § 26-51-815. Capital gains and losses
	href: https://codes.findlaw.com/ar/title-26-taxation/ar-code-sect-26-51-815.html
	- title: Arkansas 2021 AR1000D
	href: https://www.dfa.arkansas.gov/images/uploads/incomeTaxOffice/2021_AR1000D_CapitalGains.pdf#page=1
	- title: Arkansas 2022 AR1000D
	href: https://www.dfa.arkansas.gov/images/uploads/incomeTaxOffice/2022_AR1000D_CapitalGains.pdf#page=1
	- title: Arkansas 2023 AR1000D
	href: https://www.taxformfinder.org/forms/2023/2023-arkansas-form-ar1000d.pdf#page=1
	JOINT:
	# $3,000 total if filing jointly
	2021-01-01: 1_500
	HEAD_OF_HOUSEHOLD:
	2021-01-01: 1_500
	SURVIVING_SPOUSE:
	2021-01-01: 1_500
	SINGLE:
	2021-01-01: 1_500
	SEPARATE:
	2021-01-01: 1_500

.
.
As a result, Policyengine-US 0.749.1 fails the following simple unit test:

- name: AR taxable capital gains unit test 2
  absolute_error_margin: 0.01
  period: 2021
  input:
    filing_status: SINGLE
    long_term_capital_gains: -4_000
    state_fips: 5  # AR
  output:  # expected results from filing out 2021 AR1000D form
    ar_taxable_capital_gains: -3_000