Drop support for ancient gtest versions

[AlanGriffiths]

No description provided.

[codecov]

Codecov Report

Merging #3038 (cc70a5c) into main (4dd5338) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #3038      +/-   ##
==========================================
- Coverage   77.70%   77.70%   -0.01%     
==========================================
  Files        1056     1056              
  Lines       73394    73394              
==========================================
- Hits        57034    57031       -3     
- Misses      16360    16363       +3     

Files Changed	Coverage Δ
tests/include/mir/test/input_config_matchers.h	78.04% <ø> (ø)
tests/unit-tests/graphics/test_shm_buffer.cpp	94.94% <ø> (ø)

... and 6 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[Saviq]

If this blends, it blends!