Pin transitive dependency 'http' to version 0.2.6

[notmandatory]

Description

This is required because http (a transitive dependency of reqwest) changed their MSRV to 1.49 and bdk MSRV is still 1.46.

Notes to the reviewers

The http dependency MSRV was change in http version 0.2.7 released on April 28, 2022.

% cargo tree --all-features -i http                                       
http v0.2.7
├── bdk v0.19.0-dev (/home/steve/git/notmandatory/bdk)
├── h2 v0.3.13
│   ├── hyper v0.14.18
│   │   ├── hyper-tls v0.5.0
│   │   │   └── reqwest v0.11.10
│   │   │       └── bdk v0.19.0-dev (/home/steve/git/notmandatory/bdk)
│   │   └── reqwest v0.11.10 (*)
│   └── reqwest v0.11.10 (*)
├── http-body v0.4.4
│   ├── hyper v0.14.18 (*)
│   └── reqwest v0.11.10 (*)
├── hyper v0.14.18 (*)
└── reqwest v0.11.10 (*)

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

New Features:

• I've added tests for the new feature
• I've added docs for the new feature
• I've updated CHANGELOG.md

Bugfixes:

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[notmandatory]

Closing in favor of #593 which will bump MSRV to 1.51 for rust-electrum-client feature.