Bump protobuf from 3.13.0 to 3.15.3

[dependabot]

Bumps protobuf from 3.13.0 to 3.15.3.

Release notes

Sourced from protobuf's releases.

Protocol Buffers v3.15.3

Ruby

• Ruby <2.7 now uses WeakMap too, which prevents memory leaks. (#8341)

Protocol Buffers v3.15.2

Ruby

• Fix for FieldDescriptor.get(msg) (#8330)

C++

• Fix PROTOBUF_CONSTINIT macro redefinition (#8323)

Protocol Buffers v3.15.1

Ruby

• Bugfix for Message.[] for repeated or map fields (#8313)
• Fix for truncating behavior when converting Float to Duration (#8320)

C++

• Small fixes for MinGW and for C++20 with GCC (#8318)

Protocol Buffers v3.15.0

Protocol Compiler

• Optional fields for proto3 are enabled by default, and no longer require the --experimental_allow_proto3_optional flag.

C++

• MessageDifferencer: fixed bug when using custom ignore with multiple unknown fields
• Use init_seg in MSVC to push initialization to an earlier phase.
• Runtime no longer triggers -Wsign-compare warnings.
• Fixed -Wtautological-constant-out-of-range-compare warning.
• DynamicCastToGenerated works for nullptr input for even if RTTI is disabled
• Arena is refactored and optimized.
• Clarified/specified that the exact value of Arena::SpaceAllocated() is an implementation detail users must not rely on. It should not be used in unit tests.
• Change the signature of Any::PackFrom() to return false on error.
• Add fast reflection getter API for strings.
• Constant initialize the global message instances
• Avoid potential for missed wakeup in UnknownFieldSet
• Now Proto3 Oneof fields have "has" methods for checking their presence in C++.
• Bugfix for NVCC
• Return early in _InternalSerialize for empty maps.
• Adding functionality for outputting map key values in proto path logging output (does not affect comparison logic) and stop printing 'value' in the path. The modified print functionality is in the MessageDifferencer::StreamReporter.
• Fixed protocolbuffers/protobuf#8129
• Ensure that null char symbol, package and file names do not result in a crash.

... (truncated)

Commits

• 983d115 Update protobuf version
• eb542e6 Updated CHANGES.txt for 3.15.3 release
• 80ec787 Merge pull request #8341 from haberman/ruby-2.5-gc
• 9879f42 Ruby <2.7now uses WeakMap too, which prevents memory leaks.
• d7e943b Update protobuf version
• 1af4657 Updated CHANGES.txt
• 09f94e7 Fix PROTOBUF_CONSTINIT macro redifinition
• 2ff31d3 Merge pull request #8330 from haberman/rubyfix
• 4e3ea74 [Ruby] Fix for FieldDescriptor.get(msg).
• 052dc79 Update protobuf version
• Additional commits viewable in compare view

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[dependabot]

Superseded by #17.