docs: update link to Spearbit audit in README and add date to C4 audit

[AustinGreen]

Motivation:

This PR cleans up a couple audit-related documentation.

Modifications:

Use the correct link for the August Spearbit audit and add the published date to the Code4rena audit.

Result:

The link to the August Spearbit audit will work and the Code4rena audit will have the published date.

[github-actions[bot]]

Coverage after merging austin/doc-updates into main will be

84.38%

Coverage Report

File	Stmts	Branches	Funcs	Lines	Uncovered Lines
src
LlamaCore.sol	99.31%	97.44%	100%	100%	299, 399
LlamaExecutor.sol	80%	50%	100%	100%	33
LlamaFactory.sol	100%	100%	100%	100%
LlamaLens.sol	72.09%	20%	100%	82.61%	174–175, 178, 178, 178–179, 179, 179–180, 180, 180, 188
LlamaPolicy.sol	91.53%	88.89%	94.59%	91.38%	353, 392, 392, 392–394, 394, 394, 396–399, 401, 419
LlamaPolicyMetadata.sol	100%	100%	100%	100%
src/accounts
LlamaAccount.sol	100%	100%	100%	100%
src/lib
ERC721NonTransferableMinimalProxy.sol	70.42%	72.73%	72.73%	68.42%	102, 104, 106, 118–120, 190, 88, 88, 88, 90, 90, 90, 92, 92, 92, 97, 99
LlamaUtils.sol	100%	100%	100%	100%
PolicyholderCheckpoints.sol	55.88%	50%	81.82%	53.62%	130, 184–186, 186, 186–187, 189, 192, 222, 229, 229–231, 233, 233–235, 237, 237–239, 241, 241–243, 262, 265–271, 278, 46, 46–48, 48, 48–49, 51
SupplyCheckpoints.sol	57.14%	50%	83.33%	54.93%	131, 183–185, 185, 185–186, 188, 191, 235, 242, 242–244, 246, 246–248, 250, 250–252, 254, 254–256, 275, 278–284, 291, 50, 50–52, 52, 52–53, 55
src/llama-scripts
LlamaGovernanceScript.sol	50%	33.33%	43.75%	53.45%	107–108, 120–122, 132–134, 146–149, 159–161, 176–180, 190–191, 203–205, 71, 78, 78, 80, 96–97
src/strategies/absolute
LlamaAbsolutePeerReview.sol	100%	100%	100%	100%
LlamaAbsoluteQuorum.sol	100%	100%	100%	100%
LlamaAbsoluteStrategyBase.sol	94.81%	87.50%	90.91%	98%	243, 246, 296
src/strategies/relative
LlamaRelativeHolderQuorum.sol	91.67%	75%	100%	100%	52, 59
LlamaRelativeQuantityQuorum.sol	0%	0%	0%	0%	28, 28, 28–30, 42, 42, 42–44, 51–52, 52, 52–53, 58–59, 59, 59–60
LlamaRelativeStrategyBase.sol	97.62%	90.91%	100%	100%	208, 310
LlamaRelativeUniqueHolderQuorum.sol	93.33%	83.33%	100%	100%	54, 61