fix: increase max buffer size of git output

[danielroe]

we were encountering failures after merging in 1.x and 2.x commit history into nuxt main branch. this seems to be because of the default max buffer size (which is 200Kb).

this bumps the buffer size to 10Mb (we actually need 2Mb in nuxt, but this should offer some space)

for example (in another project where I used changelogen programmatically):

 ERROR  spawnSync /bin/sh ENOBUFS

    at Object.spawnSync (node:internal/child_process:1120:20)
    at spawnSync (node:child_process:910:24)
    at execSync (node:child_process:991:15)
    at execCommand (/Users/daniel/code/danielroe/rerun/node_modules/.pnpm/[email protected][email protected]/node_modules/changelogen/dist/shared/changelogen.D-9f3HTX.mjs:14:10)
    at getGitDiff (/Users/daniel/code/danielroe/rerun/node_modules/.pnpm/[email protected][email protected]/node_modules/changelogen/dist/shared/changelogen.D-9f3HTX.mjs:42:13)
    at getCommitsBetween (/Users/daniel/code/danielroe/rerun/src/commands/compare-branches.ts:44:30)
    at async Object.run (/Users/daniel/code/danielroe/rerun/src/commands/compare-branches.ts:213:27)
    at async runCommand (/Users/daniel/code/danielroe/rerun/node_modules/.pnpm/[email protected]/node_modules/citty/dist/index.mjs:316:16)
    at async runCommand (/Users/daniel/code/danielroe/rerun/node_modules/.pnpm/[email protected]/node_modules/citty/dist/index.mjs:307:11)
    at async runMain (/Users/daniel/code/danielroe/rerun/node_modules/.pnpm/[email protected]/node_modules/citty/dist/index.mjs:445:7)