IMDS fails on GitHub Actions runner

[omus]

I noticed this when adding some doctests. We may need to do some improved detection to determine if the webserver is the IMDS server.

Issue encountered:

Error: doctest failure in ~/work/AWS.jl/AWS.jl/src/AWS.jl:148-158

```jldoctest service
julia> using AWS: @service

julia> @service STS
STS

julia> STS.get_caller_identity()
OrderedCollections.LittleDict{Union{String, Symbol}, Any, Vector{Union{String, Symbol}}, Vector{Any}} with 2 entries:
  "GetCallerIdentityResult" => LittleDict{Union{String, Symbol}, Any, Vector{Un…
  "ResponseMetadata"        => LittleDict{Union{String, Symbol}, Any, Vector{Un…
```

Subexpression:

STS.get_caller_identity()

Evaluated output:

ERROR: HTTP.Exceptions.StatusError(400, "PUT", "/latest/api/token", HTTP.Messages.Response:
"""
HTTP/1.1 400 Bad Request
Content-Type: text/xml; charset=utf-8
Server: Microsoft-IIS/10.0
Date: Thu, 12 Jun 2025 16:13:12 GMT
Content-Length: 322

<?xml version="1.0" encoding="utf-8"?>
<Error xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <Code>InvalidHttpVerb</Code>
    <Message>The HTTP verb specified was not recognized by the server.</Message>
    <Details>'PUT' is not a supported verb.</Details>
</Error>""")
Stacktrace:
  [1] refresh_token!(session::AWS.IMDS.Session, duration::Int16)
    @ AWS.IMDS ~/work/AWS.jl/AWS.jl/src/IMDS.jl:94
  [2] refresh_token!
    @ ~/work/AWS.jl/AWS.jl/src/IMDS.jl:53 [inlined]
  [3] request(session::AWS.IMDS.Session, method::String, path::String; kwargs::@Kwargs{})
    @ AWS.IMDS ~/work/AWS.jl/AWS.jl/src/IMDS.jl:104
  [4] request
    @ ~/work/AWS.jl/AWS.jl/src/IMDS.jl:100 [inlined]
  [5] get(session::AWS.IMDS.Session, path::String)
    @ AWS.IMDS ~/work/AWS.jl/AWS.jl/src/IMDS.jl:168
  [6] get
    @ ~/work/AWS.jl/AWS.jl/src/IMDS.jl:180 [inlined]
  [7] ec2_instance_credentials(profile::String)
    @ AWS ~/work/AWS.jl/AWS.jl/src/AWSCredentials.jl:233
  [8] (::AWS.var"#12#18"{String})()
    @ AWS ~/work/AWS.jl/AWS.jl/src/AWSCredentials.jl:132
  [9] AWS.AWSCredentials(; profile::Nothing, throw_cred_error::Bool)
    @ AWS ~/work/AWS.jl/AWS.jl/src/AWSCredentials.jl:138
 [10] AWSCredentials
    @ ~/work/AWS.jl/AWS.jl/src/AWSCredentials.jl:113 [inlined]
 [11] AWS.AWSConfig()
    @ AWS ~/work/AWS.jl/AWS.jl/src/AWSConfig.jl:32
 [12] #global_aws_config#89
    @ ~/work/AWS.jl/AWS.jl/src/AWS.jl:82 [inlined]
 [13] global_aws_config
    @ ~/work/AWS.jl/AWS.jl/src/AWS.jl:80 [inlined]
 [14] get_caller_identity()
    @ STS ~/work/AWS.jl/AWS.jl/src/services/sts.jl:722
 [15] top-level scope
    @ none:1

Expected output:

OrderedCollections.LittleDict{Union{String, Symbol}, Any, Vector{Union{String, Symbol}}, Vector{Any}} with 2 entries:
  "GetCallerIdentityResult" => LittleDict{Union{String, Symbol}, Any, Vector{Un…
  "ResponseMetadata"        => LittleDict{Union{String, Symbol}, Any, Vector{Un…

Originally posted by @omus in #720 (comment)