Bump version to 20.3.0 (#1222)

### What
Bump version to 20.3.0, creating release branch.

### Why
Triggered by @sisuresh in
https://github.com/stellar/rs-soroban-sdk/actions/runs/7762186957.

### What is next

See the release instructions for a full rundown on the release process:
https://github.com/stellar/actions/blob/main/README-rust-release.md

Commit any changes to the `release/v20.3.0` branch that are needed in
this release.

If this is a regular release releasing from `main`, merge this PR when
ready, and after merging, create a release for this version by going to
this link:
https://github.com/stellar/rs-soroban-sdk/releases/new?tag=v20.3.0&title=20.3.0

If this is a backport or patch release of a past version, see the
release instructions. When ready to release this branch create a release
by going to this link:

https://github.com/stellar/rs-soroban-sdk/releases/new?tag=v20.3.0&title=20.3.0&target=release/v20.3.0

---------

Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Siddharth Suresh <siddharth@stellar.org>

Author: github-actions[bot]

Cargo.lock

@@ -29,39 +29,37 @@ members = [
 ]
 
 [workspace.package]
-version = "20.2.0"
+version = "20.3.0"
 rust-version = "1.74.0"
 
 [workspace.dependencies]
-soroban-sdk = { version = "20.2.0", path = "soroban-sdk" }
-soroban-sdk-macros = { version = "20.2.0", path = "soroban-sdk-macros" }
-soroban-spec = { version = "20.2.0", path = "soroban-spec" }
-soroban-spec-rust = { version = "20.2.0", path = "soroban-spec-rust" }
-soroban-ledger-snapshot = { version = "20.2.0", path = "soroban-ledger-snapshot" }
-soroban-token-sdk = { version = "20.2.0", path = "soroban-token-sdk" }
+soroban-sdk = { version = "20.3.0", path = "soroban-sdk" }
+soroban-sdk-macros = { version = "20.3.0", path = "soroban-sdk-macros" }
+soroban-spec = { version = "20.3.0", path = "soroban-spec" }
+soroban-spec-rust = { version = "20.3.0", path = "soroban-spec-rust" }
+soroban-ledger-snapshot = { version = "20.3.0", path = "soroban-ledger-snapshot" }
+soroban-token-sdk = { version = "20.3.0", path = "soroban-token-sdk" }
 
 [workspace.dependencies.soroban-env-common]
-version = "=20.1.1"
+version = "=20.2.0"
 git = "https://github.com/stellar/rs-soroban-env"
-rev = "096d4614299ac08c93d255a5482dd079873265dd"
+rev = "1bfc0f2a2ee134efc1e1b0d5270281d0cba61c2e"
 
 [workspace.dependencies.soroban-env-guest]
-version = "=20.1.1"
+version = "=20.2.0"
 git = "https://github.com/stellar/rs-soroban-env"
-rev = "096d4614299ac08c93d255a5482dd079873265dd"
+rev = "1bfc0f2a2ee134efc1e1b0d5270281d0cba61c2e"
 
 [workspace.dependencies.soroban-env-host]
-version = "=20.1.1"
+version = "=20.2.0"
 git = "https://github.com/stellar/rs-soroban-env"
-rev = "096d4614299ac08c93d255a5482dd079873265dd"
+rev = "1bfc0f2a2ee134efc1e1b0d5270281d0cba61c2e"
 
 [workspace.dependencies.stellar-strkey]
 version = "=0.0.8"
 
 [workspace.dependencies.stellar-xdr]
-version = "=20.0.2"
-# git = "https://github.com/stellar/rs-stellar-xdr"
-# rev = "a928e82943e4e93c887555fdec3b1e139ad810d2"
+version = "=20.1.0"
 default-features = false
 features = ["curr"]