Update lightning requirement from >=2.0.0 to >=2.6.4

[dependabot]

Updates the requirements on lightning to permit the latest version.

Release notes

Sourced from lightning's releases.

Lightning 2.6.4

Changes in 2.6.4

PyTorch Lightning

• Removed support for Neptune logger (#21572).

Note: We usually don't remove features in a patch release, however in this case it's an exception since even without removing it the integration would be broken due to Neptune being acquired and sunsetting public service

• Raised minimum LitLogger version to 2026-03-17 (#21591)

• Fixed val_check_interval raising ValueError when limit_val_batches=0 and interval exceeds training batches (#21560)
• Fixed FSDP mixed precision (bf16-mixed, 16-mixed) initializing model parameters in half precision instead of fp32 (#21586)
• Fixed device_mesh type hint in FSDPStrategy to accept a 2-element tuple via the CLI (#21581)
• Fixed RichModelSummary model size display formatting (#21467)
• Fixed floating-point precision in SimpleProfiler duration aggregation by using math.fsum (#21525)

Lightning Fabric

• Fixed FSDP mixed precision (bf16-mixed, 16-mixed) initializing model parameters in half precision instead of fp32 (#21586)
• Fixed device_mesh type hint in FSDPStrategy to accept a 2-element tuple via the CLI (#21581)

Full commit list: 2.6.1 -> 2.6.4

Contributors

New Contributors

• @​AsherJingkongChen made their first contribution in Lightning-AI/pytorch-lightning#21467
• @​ManasVardhan made their first contribution in Lightning-AI/pytorch-lightning#21560

... (truncated)

Commits

• 43a4411 Pin PyPI publish action for trusted publishing (#21731)
• c016e62 Cherry-pick publishing changes to release/stable (#21727)
• 458c50a ci: disable litbot checkgroup (#21728)
• 9f074af Prepare Release Note for 2.6.2 Release (#21592)
• 73f593d Remove NeptuneLogger integration from PyTorch Lightning (#21572)
• 1690c21 Update Litlogger Integration to latest version (#21591)
• 6c92678 fix: FSDP mixed precision initializes params in fp32, not bf16/fp16 (#21586)
• a13361d build(deps): update rich requirement from <14.3.0,>=12.3.0 to >=12.3.0,<14.4....
• 5730e81 build(deps): update nbconvert requirement from <7.17,>7.14 to >7.14,<7.18 in ...
• df28744 build(deps): bump Lightning-AI/utilities/.github/workflows/check-schema.yml f...
• Additional commits viewable in compare view

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