Fix SPDX-License-Identifier in header comments

[jdisanti]

Motivation and Context

@hyandell pointed out the SPDX-License-Identifier has an unnecessary trailing period in awslabs/aws-sdk-kotlin#601, and I think we must have copied the license header from that repository at some point in the early days of smithy-rs. This PR removes the trailing period and updates our linter.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[github-actions]

A new generated diff is ready to view.

• AWS SDK (ignoring whitespace)
• Server Test (ignoring whitespace)

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Rust Wrk benchmark report:

Duration: 90 sec, Connections: 32, Threads: 2

Measurement	Deviation	Current	Old
Requests/sec	5.88%	82218.8	77650.12
Total requests	5.87%	7401831	6991721
Total errors	NaN%	0	0
Total successes	5.87%	7401831	6991721
Average latency ms	27.66%	1.2	0.94
Minimum latency ms	0.00%	0.02	0.02
Maximum latency ms	58.47%	34.34	21.67
Stdev latency ms	30.67%	2.13	1.63
Transfer Mb	5.87%	769.42	726.79
Connect errors	NaN%	0	0
Read errors	NaN%	0	0
Write errors	NaN%	0	0
Status errors (not 2xx/3xx)	NaN%	0	0
Timeout errors	NaN%	0	0

[crisidev]

Nice sed and replace :)

[rcoh]

LGTM! this really gave chrome a run for its money 😅