* contracts-bedrock: attempt to fix flake

The xdm invariant tests are failing, attempt to fix through
ensuring that proxies are ignored.

Example result of a failing test:

```
Failing tests:
Encountered 1 failing test in test/invariants/CrossDomainMessenger.t.sol:XDM_MinGasLimits_Reverts
[FAIL. Reason: <empty revert data>]
[Sequence]
sender=0x420000000000000000000000000000000000078C addr=[test/invariants/CrossDomainMessenger.t.sol:RelayActor]0x22b24e3bBa3087f537d2E35f8E2F1E9a257eAa98 calldata=relay(uint8,uint8,bytes) args=[97, 74, 0x0000000000000000000000000000000000000000000000000000000000001e4c]
sender=0x0000000000000000000000000000000000002f8D addr=0x420000000000000000000000000000000000078C calldata=0x4f1ef28600000000000000000000000000000000000000000000000000000000000025f800000000000000000000000000000000000000000000000000000000000000400000000000000000000000000000000000000000000000000000000000000020000000000000000000000000000000000000000000000000000000000000180e args=[]
sender=0x00000000000000000000000000000000000010e4 addr=[test/invariants/CrossDomainMessenger.t.sol:RelayActor]0x22b24e3bBa3087f537d2E35f8E2F1E9a257eAa98 calldata=relay(uint8,uint8,bytes) args=[254, 3, 0x08daedb9c7ea07d62e421fe926b7d73f04b73c8fd120be847e937abf2659f31e4137dabd04c355a93fd71b78050a02f12e1ab7d353]
sender=0x0000000000000000000000000000000000001533 addr=0x420000000000000000000000000000000000078C calldata=0x4f1ef2860000000000000000000000002dfbf40ac423099dff1d47cbf2198311a132084b00000000000000000000000000000000000000000000000000000000000000400000000000000000000000000000000000000000000000000000000000000020c32e06324e64ab299df2856f5d081a93b30c98764b1fac5213339a070c13a0a4 args=[]
sender=0x0000000000000000000000000000000018160Ddc addr=[test/invariants/CrossDomainMessenger.t.sol:RelayActor]0x22b24e3bBa3087f537d2E35f8E2F1E9a257eAa98 calldata=relay(uint8,uint8,bytes) args=[10, 12, 0x1998c6d2b9539a719f8393a7bd3a90611f940901e3f2ddc44866d450f60a21b99391b804ea77473a42c7e869123cb61c2f137f3f9116568a4709a86615d0617555]
sender=0x6F77000000000000000000000000000000000001 addr=[test/invariants/CrossDomainMessenger.t.sol:RelayActor]0x22b24e3bBa3087f537d2E35f8E2F1E9a257eAa98 calldata=relay(uint8,uint8,bytes) args=[1, 0, 0x3ce36e01a862e656ef6d7e534c604f7371751d22722f7d27382b5bc92b1b926dacb6fe80]
sender=0x3D7Ebc40AF7092E3F1C81F2e996cbA5Cae2090d7 addr=0x420000000000000000000000000000000000078C calldata=0x8f283970000000000000000000000000f0cc4c31297072a46cdf740fbfaf9d6d35017c06 args=[]
sender=0xB80194025AeE4A9126B156619C8943372b72dA2b addr=[test/invariants/CrossDomainMessenger.t.sol:RelayActor]0x22b24e3bBa3087f537d2E35f8E2F1E9a257eAa98 calldata=relay(uint8,uint8,bytes) args=[0, 1, 0xeca8d0fabc96e0c64ec9faed41e05a5a0cb6ebb9de5c5f]
 invariant_minGasLimits() (runs: 256, calls: 8168, reverts: 2278)

Encountered a total of 1 failing tests, 879 tests succeeded
```

I believe the issue is `addr=0x420000000000000000000000000000000000078C` - A predeploy is set to
`addr`. Not sure if this will 100% fix the issue but first attempt.

* docs: fix